Three-dimensional memory array including self-aligned
dielectric pillar structures and methods of making the same.

ABSTRACT

An alternating stack of insulating layers and spacer material layers is formed over a substrate. Memory stack structures are formed through the alternating stack. A pair of backside trenches and a set of nested trenches are simultaneously formed through the alternating stack. Each trench within the set of nested trenches is spaced from any other trench within the set of nested trenches by at least one patterned remaining portion of the alternating stack having a respective shape of an enclosing wall. The at least one patterned remaining portion of the alternating stack is removed from inside to outside using sequential etch processes. A dielectric pillar structure is formed within the pillar-shaped cavity. The sacrificial material layers are replaced with electrically conductive layers. A through-memory-level conductive via structure is formed through the dielectric pillar structure.

FIELD

The present disclosure relates generally to the field of semiconductordevices and specifically to a three-dimensional memory device includinga dielectric pillar structure and methods of making the same.

BACKGROUND

A three-dimensional memory device including three-dimensional verticalNAND strings having one bit per cell is disclosed in an article by T.Endoh et al., titled “Novel Ultra High Density Memory With AStacked-Surrounding Gate Transistor (S-SGT) Structured Cell”, IEDM Proc.(2001) 33-36. Recently, ultra-high-density storage devices usingthree-dimensional (3D) memory stack structures have been proposed. Thememory stack structures overlie a substrate and extend through analternating stack of insulating layers and electrically conductivelayers. The memory stack structures include vertically stacks of memoryelements provided at levels of the electrically conductive layers.Peripheral devices may be provided on the substrate underneath thealternating stack and the memory stack structures.

SUMMARY

According to an embodiment of the present disclosure, a method offorming a semiconductor structure is provided, which may comprise thesteps of: forming an alternating stack of insulating layers andsacrificial material layers over a substrate; forming memory stackstructures through the alternating stack; simultaneously forming a pairof backside trenches and a set of nested trenches through thealternating stack around the memory stack structures, wherein eachtrench within the set of nested trenches is spaced from any other trenchwithin the set of nested trenches by at least one patterned remainingportion of the alternating stack having a respective shape of anenclosing wall; removing the at least one patterned remaining portion ofthe alternating stack using at least one etchant while preventing accessof the at least one etchant to the pair of backside trenches, wherein apillar-shaped cavity including all volumes of the set of nested trenchesand the at least one patterned remaining portion of the alternatingstack is formed; forming a dielectric pillar structure within thepillar-shaped cavity; replacing remaining portions of the sacrificialmaterial layers with electrically conductive layers; and forming athrough-memory-level conductive via structure through the dielectricpillar structure.

According to another embodiment of the present disclosure, a method offorming a semiconductor structure comprises forming an alternating stackof insulating layers and sacrificial material layers over a substrate,forming memory stack structures comprising a vertical semiconductorchannel and a memory film through the alternating stack, simultaneouslyforming a pair of backside trenches and a set of nested trenches throughthe alternating stack around the memory stack structures, wherein eachtrench within the set of nested trenches is spaced from any other trenchwithin the set of nested trenches by at least one patterned remainingportion of the alternating stack, forming a pair of sacrificial backsidetrench fill material structures in the pair of backside trenches andsacrificial nested trench fill structures in the set of nested trenchesconcurrently with formation of the pair of sacrificial backside trenchfill material structures, forming an etch mask layer over the pair ofsacrificial backside trench fill material structures and the set ofsacrificial nested trench fill structures, forming an opening in theetch mask layer which exposes sacrificial inner trench fill structure ofthe set of sacrificial nested trench fill, while a sacrificial outertrench fill structure of the set of sacrificial nested trench fillstructures and the pair of sacrificial backside trench fill materialstructures are covered by the etch mask layer, removing the sacrificialinner trench fill structure through the opening selective to the atleast one patterned remaining portion of the alternating stack to form avoid, removing the at least one patterned remaining portion of thealternating stack that is physically exposed to the opening and to thevoid, removing the sacrificial outer trench fill structure through theopening after the step of removing the at least one patterned remainingportion of the alternating stack, forming a dielectric pillar structurewithin the pillar-shaped cavity, removing the etch mask layer over thepair of sacrificial backside trench fill material structures, removingthe pair of sacrificial backside trench fill material structures fromthe pair of backside trenches, replacing the sacrificial material layersof the alternating stack with electrically conductive layers through thepair of backside trenches, and forming a through-memory-level conductivevia structure through the dielectric pillar structure.

According to another embodiment of the present disclosure, asemiconductor structure is provided, which may comprise: a semiconductormaterial layer overlying a substrate; an alternating stack of insulatinglayers and electrically conductive layers located over the semiconductormaterial layer; memory stack structures may vertically extend throughthe alternating stack; a peripheral circuitry may include field effecttransistors and located over the substrate and underneath thesemiconductor material layer; lower-level metal interconnect structuresmay be formed in lower-level dielectric material layers and locatedbetween the peripheral circuitry and the semiconductor material layer; apair of backside trench fill structures may vertically extend throughthe alternating stack and laterally extend along a first horizontaldirection; a dielectric pillar structure may extend through thealternating stack and located between the pair of backside trench fillstructures, wherein each of the pair of backside trench fill structuresand the dielectric pillar structure comprises sidewalls having a bowingprofile that provides a greater width at a height between a topmostlayer of the alternating stack and a bottommost layer of the alternatingstack than at a height of the topmost layer of the alternating stack;and a through-memory-level conductive via structure vertically extendingthrough the dielectric pillar structure and an opening in thesemiconductor material layer and contacting one of the lower-level metalinterconnect structures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a vertical cross-sectional view of an exemplary structureafter formation of semiconductor devices, lower level dielectric layers,lower metal interconnect structures, and in-process source levelmaterial layers on a semiconductor substrate according to a firstembodiment of the present disclosure.

FIG. 1B is a top-down view of the exemplary structure of FIG. 1A. Thehinged vertical plane A-A′ is the plane of the vertical cross-sectionalview of FIG. 1A.

FIG. 1C is a magnified view of the in-process source level materiallayers along the vertical plane C-C′ of FIG. 1B.

FIG. 2 is a vertical cross-sectional view of the exemplary structureafter formation of a first-tier alternating stack of first insultinglayers and first spacer material layers according to an embodiment ofthe present disclosure.

FIG. 3 is a vertical cross-sectional view of the exemplary structureafter patterning a first-tier staircase region, a first retro-steppeddielectric material portion, and an inter-tier dielectric layeraccording to an embodiment of the present disclosure.

FIG. 4A is a vertical cross-sectional view of the exemplary structureafter formation of first-tier memory openings and first-tier supportopenings according to an embodiment of the present disclosure.

FIG. 4B is a horizontal cross-sectional view of the exemplary structureof FIG. 4A. The hinged vertical plane A-A′ corresponds to the plane ofthe vertical cross-sectional view of FIG. 4A.

FIG. 5 is a vertical cross-sectional view of the exemplary structureafter formation of various sacrificial fill structures according to anembodiment of the present disclosure.

FIG. 6 is a vertical cross-sectional view of the exemplary structureafter formation of a second-tier alternating stack of second insulatinglayers and second spacer material layers, second stepped surfaces, and asecond retro-stepped dielectric material portion according to anembodiment of the present disclosure.

FIG. 7A is a vertical cross-sectional view of the exemplary structureafter formation of second-tier memory openings and second-tier supportopenings according to an embodiment of the present disclosure.

FIG. 7B is a horizontal cross-sectional of the exemplary structure alongthe horizontal plane B-B′ of FIG. 7A. The hinged vertical plane A-A′corresponds to the plane of the vertical cross-sectional view of FIG.7A.

FIG. 8 is a vertical cross-sectional view of the exemplary structureafter formation of inter-tier memory openings and inter-tier supportopenings according to an embodiment of the present disclosure.

FIGS. 9A-9D illustrate sequential vertical cross-sectional views of amemory opening during formation of a memory opening fill structureaccording to an embodiment of the present disclosure.

FIG. 10 is a vertical cross-sectional view of the exemplary structureafter formation of memory opening fill structures and support pillarstructures according to an embodiment of the present disclosure.

FIG. 11A is a vertical cross-sectional view of the exemplary structureafter formation of backside trenches and sets of nested trenchesaccording to an embodiment of the present disclosure.

FIG. 11B is a horizontal cross-sectional of the exemplary structurealong the horizontal plane B-B′ of FIG. 11A. The hinged vertical planeA-A′ corresponds to the plane of the vertical cross-sectional view ofFIG. 11A.

FIG. 11C is a magnified view of a region within the view of FIG. 11Bthat includes a pair of backside trenches, a moat trench, and contactopenings.

FIG. 11D is a vertical cross-sectional view of a trench within a set ofnested trenches along a vertical plane D-D′ of FIG. 11B.

FIG. 11E is a vertical cross-sectional view of a backside trench in theexemplary structure along a vertical plane E-E′ of FIG. 11B.

FIG. 12A is a vertical cross-sectional view of the exemplary structureafter formation of sacrificial backside trench fill material structuresand sacrificial nested trench fill structures according to an embodimentof the present disclosure.

FIG. 12B is a horizontal cross-sectional view of the exemplary structurealong the horizontal plane B-B′ of FIG. 12A. The hinged vertical planeA-A′ corresponds to the plane of the vertical cross-sectional view ofFIG. 12A.

FIG. 12C is a magnified view of a region of the horizontalcross-sectional view of FIG. 12B.

FIG. 13A is a vertical cross-sectional view of the exemplary structureafter application and patterning of a photoresist layer to form openingsthat overlie inner nested trench fill structures according to anembodiment of the present disclosure.

FIG. 13B is a top-down view of the exemplary structure of FIG. 13A.

FIG. 13C is a magnified top-down view of a region including a set ofnested trench fill structures in the exemplary structure of FIGS. 13Aand 13B.

FIG. 14A is a vertical cross-sectional view of the exemplary structureafter removal of the inner nested trench fill structures according to anembodiment of the present disclosure.

FIG. 14B is a horizontal cross-sectional view of the exemplary structurealong the plane B-B′ of FIG. 14A.

FIG. 14C is a magnified view of a region including a set of nestedtrenches in the horizontal cross-sectional view of FIG. 14B.

FIG. 15A is a vertical cross-sectional view of the exemplary structureafter removal of patterned remaining portions of the alternating stackaccording to an embodiment of the present disclosure.

FIG. 15B is a horizontal cross-sectional view of the exemplary structurealong the plane B-B′ of FIG. 15A.

FIG. 15C is a magnified view of a region including a set of nestedtrenches in the horizontal cross-sectional view of FIG. 15B.

FIG. 15D is a top-down view of the exemplary structure of FIGS. 15A-15C.

FIG. 16A is a vertical cross-sectional view of the exemplary structureafter removal of sacrificial outer trench fill structures according toan embodiment of the present disclosure.

FIG. 16B is a horizontal cross-sectional view of the exemplary structurealong the plane B-B′ of FIG. 16A.

FIG. 16C is a magnified view of a region including a set of nestedtrenches in the horizontal cross-sectional view of FIG. 15B.

FIG. 17A is a vertical cross-sectional view of the exemplary structureafter formation of dielectric pillar structures according to anembodiment of the present disclosure.

FIG. 17B is a horizontal cross-sectional view of the exemplary structurealong the plane B-B′ of FIG. 17A.

FIG. 17C is a magnified view of a region including a set of nestedtrenches in the horizontal cross-sectional view of FIG. 17B.

FIG. 18 is a vertical cross-sectional view of the exemplary structureafter removal of the sacrificial backside trench fill materialstructures according to an embodiment of the present disclosure.

FIGS. 19A-19E illustrate sequential vertical cross-sectional views ofmemory opening fill structures and a backside trench during replacementof the in-process source-level material layers with source-levelmaterial layers according to an embodiment of the present disclosure.

FIG. 20 is a vertical cross-sectional view of the exemplary structureafter formation of source-level material layers according to anembodiment of the present disclosure.

FIG. 21 is a vertical cross-sectional view of the exemplary structureafter formation of backside recesses according to an embodiment of thepresent disclosure.

FIG. 22 is a vertical cross-sectional view of the exemplary structureafter formation of electrically conductive layers according to anembodiment of the present disclosure.

FIG. 23A is a vertical cross-sectional view of the exemplary structureafter formation of backside trench fill structures according to anembodiment of the present disclosure.

FIG. 23B is a horizontal cross-sectional of the exemplary structurealong the horizontal plane B-B′ of FIG. 23A. The hinged vertical planeA-A′ corresponds to the plane of the vertical cross-sectional view ofFIG. 23A.

FIG. 23C is a vertical cross-sectional view of the exemplary structurealong the vertical plane C-C′ of FIG. 23B.

FIG. 23D is a horizontal cross-sectional view of the exemplary structurealong the horizontal plane D-D′ of FIG. 23A.

FIG. 24 is a vertical cross-sectional view of the exemplary structureafter formation of contact via cavities according to an embodiment ofthe present disclosure.

FIG. 25 is a vertical cross-sectional view of the exemplary structureafter formation of first through-memory-level conductive via structureaccording to an embodiment of the present disclosure.

FIG. 26A is a vertical cross-sectional view of the exemplary structureafter formation of a second contact level dielectric layer and variousadditional contact via structures according to an embodiment of thepresent disclosure.

FIG. 26B is a horizontal cross-sectional view of the exemplary structurealong the vertical plane B-B′ of FIG. 26A. The hinged vertical planeA-A′ corresponds to the plane of the vertical cross-sectional view ofFIG. 26A.

FIG. 26C is a magnified view of a region of the horizontalcross-sectional view of FIG. 24B.

FIG. 26D is a horizontal cross-sectional view of the exemplary structurealong the horizontal plane D-D′ of FIG. 26B.

FIG. 27 is a vertical cross-sectional view of the exemplary structureafter formation of upper-level metal line structures according to anembodiment of the present disclosure.

DETAILED DESCRIPTION

As discussed above, the present invention is directed to athree-dimensional memory device including a self-aligned dielectricpillar structure and methods of making the same, various embodiments ofwhich are described herein in detail. The various embodiments of thepresent disclosure may be used to form a three-dimensional memory devicesuch as a three-dimensional NAND memory array including a self-aligneddielectric pillar structure formed within an alternating stack ofinsulating layers and electrically conductive layers.

The drawings are not drawn to scale. Multiple instances of an elementmay be duplicated where a single instance of the element is illustrated,unless absence of duplication of elements is expressly described orclearly indicated otherwise. Ordinals such as “first,” “second,” and“third” are used merely to identify similar elements, and differentordinals may be used across the specification and the claims of theinstant disclosure. The same reference numerals refer to the sameelement or similar element. Unless otherwise indicated, elements havingthe same reference numerals are presumed to have the same compositionand the same function. Unless otherwise indicated, a “contact” betweenelements refers to a direct contact between elements that provides anedge or a surface shared by the elements. As used herein, a firstelement located “on” a second element may be located on the exteriorside of a surface of the second element or on the interior side of thesecond element. As used herein, a first element is located “directly on”a second element if there exist a physical contact between a surface ofthe first element and a surface of the second element. As used herein, a“prototype” structure or an “in-process” structure refers to a transientstructure that is subsequently modified in the shape or composition ofat least one component therein.

As used herein, a “layer” refers to a material portion including aregion having a thickness. A layer may extend over the entirety of anunderlying or overlying structure, or may have an extent less than theextent of an underlying or overlying structure. Further, a layer may bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer may be located between any pair of horizontal planesbetween or at a top surface and a bottom surface of the continuousstructure. A layer may extend horizontally, vertically, and/or along atapered surface. A substrate may be a layer, may include one or morelayers therein, and/or may have one or more layer thereupon, thereabove,and/or therebelow.

As used herein, a first surface and a second surface are “verticallycoincident” with each other if the second surface overlies or underliesthe first surface and there exists a vertical plane or a substantiallyvertical plane that includes the first surface and the second surface. Asubstantially vertical plane is a plane that extends straight along adirection that deviates from a vertical direction by an angle less than5 degrees. A vertical plane or a substantially vertical plane isstraight along a vertical direction or a substantially verticaldirection, and may, or may not, include a curvature along a directionthat is perpendicular to the vertical direction or the substantiallyvertical direction.

As used herein, a “memory level” or a “memory array level” refers to thelevel corresponding to a general region between a first horizontal plane(i.e., a plane parallel to the top surface of the substrate) includingtopmost surfaces of an array of memory elements and a second horizontalplane including bottommost surfaces of the array of memory elements. Asused herein, a “through-stack” element refers to an element thatvertically extends through a memory level.

As used herein, a “semiconducting material” refers to a material havingelectrical conductivity in the range from 1.0×10⁻⁵ S/m to 1.0×10⁵ S/m.As used herein, a “semiconductor material” refers to a material havingelectrical conductivity in the range from 1.0×10⁻⁵ S/m to 1.0 S/m in theabsence of electrical dopants therein, and is capable of producing adoped material having electrical conductivity in a range from 1.0 S/m to1.0×10⁷ S/m upon suitable doping with an electrical dopant. As usedherein, an “electrical dopant” refers to a p-type dopant that adds ahole to a valence band within a band structure, or an n-type dopant thatadds an electron to a conduction band within a band structure. As usedherein, a “conductive material” refers to a material having electricalconductivity greater than 1.0×10⁵ S/m. As used herein, an “insulatormaterial” or a “dielectric material” refers to a material havingelectrical conductivity less than 1.0×10⁻⁵ S/m. As used herein, a“heavily doped semiconductor material” refers to a semiconductormaterial that is doped with electrical dopant at a sufficiently highatomic concentration to become a conductive material either as formed asa crystalline material or if converted into a crystalline materialthrough an anneal process (for example, from an initial amorphousstate), i.e., to provide electrical conductivity greater than 1.0×10⁵S/m. A “doped semiconductor material” may be a heavily dopedsemiconductor material, or may be a semiconductor material that includeselectrical dopants (i.e., p-type dopants and/or n-type dopants) at aconcentration that provides electrical conductivity in the range from1.0×10⁻⁵ S/m to 1.0×10⁷ S/m. An “intrinsic semiconductor material”refers to a semiconductor material that is not doped with electricaldopants. Thus, a semiconductor material may be semiconducting orconductive, and may be an intrinsic semiconductor material or a dopedsemiconductor material. A doped semiconductor material may besemiconducting or conductive depending on the atomic concentration ofelectrical dopants therein. As used herein, a “metallic material” refersto a conductive material including at least one metallic elementtherein. All measurements for electrical conductivities are made at thestandard condition.

A monolithic three-dimensional memory array is a memory array in whichmultiple memory levels are formed above a single substrate, such as asemiconductor wafer, with no intervening substrates. The term“monolithic” means that layers of each level of the array are directlydeposited on the layers of each underlying level of the array. Incontrast, two dimensional arrays may be formed separately and thenpackaged together to form a non-monolithic memory device. For example,non-monolithic stacked memories have been constructed by forming memorylevels on separate substrates and vertically stacking the memory levels,as described in U.S. Pat. No. 5,915,167 titled “Three-dimensionalStructure Memory.” The substrates may be thinned or removed from thememory levels before bonding, but as the memory levels are initiallyformed over separate substrates, such memories are not true monolithicthree-dimensional memory arrays. The various three-dimensional memorydevices of the present disclosure include a monolithic three-dimensionalNAND string memory device, and may be fabricated using the variousembodiments described herein.

The various three-dimensional memory devices of the present disclosureinclude a monolithic three-dimensional NAND string memory device, andmay be fabricated using the various embodiments described herein. Themonolithic three-dimensional NAND string may be located in a monolithic,three-dimensional array of NAND strings located over the substrate. Atleast one memory cell in the first device level of the three-dimensionalarray of NAND strings may be located over another memory cell in thesecond device level of the three-dimensional array of NAND strings.

Generally, a semiconductor package (or a “package”) refers to a unitsemiconductor device that may be attached to a circuit board through aset of pins or solder balls. A semiconductor package may include asemiconductor chip (or a “chip”) or a plurality of semiconductor chipsthat are bonded throughout, for example, by flip-chip bonding or anotherchip-to-chip bonding. A package or a chip may include a singlesemiconductor die (or a “die”) or a plurality of semiconductor dies. Adie is the smallest unit that may independently execute externalcommands or report status. Typically, a package or a chip with multipledies is capable of simultaneously executing as many external commands asthe total number of dies therein. Each die includes one or more planes.Identical concurrent operations may be executed in each plane within asame die, although there may be some restrictions. In case a die is amemory die, i.e., a die including memory elements, concurrent readoperations, concurrent write operations, or concurrent erase operationsmay be performed in each plane within a same memory die. In a memorydie, each plane contains a number of memory blocks (or “blocks”), whichare the smallest unit that may be erased by in a single erase operation.Each memory block contains a number of pages, which are the smallestunits that may be selected for programming. A page is also the smallestunit that may be selected to a read operation.

Referring to FIGS. 1A-1C, an exemplary structure according to a firstembodiment of the present disclosure is illustrated. FIG. 1C is amagnified view of an in-process source-level material layers 10′illustrated in FIGS. 1A and 1B. The exemplary structure includes asubstrate 8 and semiconductor devices 710 formed thereupon. Thesubstrate 8 includes a substrate semiconductor layer 9 at least at anupper portion thereof. Shallow trench isolation structures 720 may beformed in an upper portion of the substrate semiconductor layer 9 toprovide electrical isolation from the semiconductor devices. Thesemiconductor devices 710 may include, for example, field effecttransistors including respective transistor active regions 742 (i.e.,source regions and drain regions), channel regions 746, and gatestructures 750. The field effect transistors may be arranged in a CMOSconfiguration. Each gate structure 750 may include, for example, a gatedielectric 752, a gate electrode 754, a dielectric gate spacer 756 and agate cap dielectric 758. The semiconductor devices 710 may include anysemiconductor circuitry to support operation of a memory structure thatmay be subsequently formed, which is typically referred to as a drivercircuitry, which is also known as peripheral circuitry.

The peripheral circuitry may be configured to control charge storageelements within memory stack structures in a three-dimensional memorydevice to be subsequently formed. As used herein, peripheral circuitryrefers to any, each, or all, of word line decoder circuitry, word lineswitching circuitry, bit line decoder circuitry, bit line sensing and/orswitching circuitry, power supply/distribution circuitry, data bufferand/or latch, or any other semiconductor circuitry that may beimplemented outside a memory array structure for a memory device. Forexample, the semiconductor devices may include word line switchingdevices for electrically biasing word lines of three-dimensional memorystructures to be subsequently formed.

Dielectric material layers are formed over the semiconductor devices710, which are herein referred to as lower-level dielectric materiallayers 760. The lower-level dielectric material layers 760 may include,for example, a dielectric liner 762 (such as a silicon nitride linerthat blocks diffusion of mobile ions and/or apply appropriate stress tounderlying structures), first dielectric material layers 764 thatoverlie the dielectric liner 762, a silicon nitride layer (e.g.,hydrogen diffusion barrier) 766 that overlies the first dielectricmaterial layers 764, and at least one second dielectric layer 768. Thedielectric layer stack including the lower-level dielectric materiallayers 760 functions as a matrix for lower-level metal interconnectstructures 780 that provide electrical wiring to and from the variousnodes of the semiconductor devices and landing pads forthrough-memory-level contact via structures to be subsequently formed.The lower-level metal interconnect structures 780 are formed within thedielectric layer stack of the lower-level dielectric material layers 760and overlies the field effect transistors. The lower-level metalinterconnect structures 780 comprise a lower-level metal line structurelocated under and optionally contacting a bottom surface of the siliconnitride layer 766. The lower-level metal interconnect structures 780 maybe formed in the lower-level dielectric material layers 760 and overliesthe peripheral circuitry.

For example, the lower-level metal interconnect structures 780 may beformed within the first dielectric material layers 764. The firstdielectric material layers 764 may be a plurality of dielectric materiallayers in which various elements of the lower-level metal interconnectstructures 780 are sequentially formed. Each dielectric material layerselected from the first dielectric material layers 764 may include anyof doped silicate glass, undoped silicate glass, organosilicate glass,silicon nitride, silicon oxynitride, and dielectric metal oxides (suchas aluminum oxide). In one embodiment, the first dielectric materiallayers 764 may comprise, or consist essentially of, dielectric materiallayers having dielectric constants that do not exceed the dielectricconstant of undoped silicate glass (silicon oxide) of 3.9. Thelower-level metal interconnect structures 780 may include various devicecontact via structures 782 (e.g., source and drain electrodes whichcontact the respective source and drain nodes of the device or gateelectrode contacts), intermediate lower-level metal line structures 784,lower-level metal via structures 786, and landing-pad-level metal linestructures 788 that are configured to function as landing pads forthrough-memory-level contact via structures to be subsequently formed.

The landing-pad-level metal line structures 788 may be formed within atopmost dielectric material layer of the first dielectric materiallayers 764 (which may be a plurality of dielectric material layers).Each of the lower-level metal interconnect structures 780 may include ametallic nitride liner and a metal fill structure. Top surfaces of thelanding-pad-level metal line structures 788 and the topmost surface ofthe first dielectric material layers 764 may be planarized by aplanarization process, such as chemical mechanical planarization. Thesilicon nitride layer 766 may be formed directly on the top surfaces ofthe landing-pad-level metal line structures 788 and the topmost surfaceof the first dielectric material layers 764.

The at least one second dielectric material layer 768 may include asingle dielectric material layer or a plurality of dielectric materiallayers. Each dielectric material layer selected from the at least onesecond dielectric material layer 768 may include any of doped silicateglass, undoped silicate glass, and organosilicate glass. In oneembodiment, the at least one first second material layer 768 maycomprise, or consist essentially of, dielectric material layers havingdielectric constants that do not exceed the dielectric constant ofundoped silicate glass (silicon oxide) of 3.9.

An optional layer of a metallic material and a layer of a semiconductormaterial may be deposited over, or within patterned recesses of, the atleast one second dielectric material layer 768, and may belithographically patterned to provide an optional conductive plate layer6 and in-process source-level material layers 10′. The optionalconductive plate layer 6, if present, provides a high conductivityconduction path for electrical current that flows into, or out of, thein-process source-level material layers 10′. The optional conductiveplate layer 6 may include a conductive material such as a metal or aheavily doped semiconductor material. The optional conductive platelayer 6, for example, may include a tungsten layer having a thickness ina range from 3 nm to 100 nm, although lesser and greater thicknesses mayalso be used. A metal nitride layer (not shown) may be provided as adiffusion barrier layer on top of the conductive plate layer 6. Theconductive plate layer 6 may function as a special source line in thecompleted device. In addition, the conductive plate layer 6 may comprisean etch stop layer and may comprise any suitable conductive,semiconductor or insulating layer. The optional conductive plate layer 6may include a metallic compound material such as a conductive metallicnitride (e.g., TiN) and/or a metal (e.g., W). The thickness of theoptional conductive plate layer 6 may be in a range from 5 nm to 100 nm,although lesser and greater thicknesses may also be used.

The in-process source-level material layers 10′ may include variouslayers that are subsequently modified to form source-level materiallayers. The source-level material layers, upon formation, include asource contact layer that functions as a common source region forvertical field effect transistors of a three-dimensional memory device.In one embodiment, the in-process source-level material layers 10′ mayinclude, from bottom to top, a lower source-level material layer 112, alower sacrificial liner 103, a source-level sacrificial layer 104, anupper sacrificial liner 105, an upper source-level semiconductor layer116, a source-level insulating layer 117, and an optionalsource-select-level conductive layer 118.

The lower source-level material layer 112 and the upper source-levelsemiconductor layer 116 may include a doped semiconductor material suchas doped polysilicon or doped amorphous silicon. The conductivity typeof the lower source-level material layer 112 and the upper source-levelsemiconductor layer 116 may be the opposite of the conductivity ofvertical semiconductor channels to be subsequently formed. For example,if the vertical semiconductor channels to be subsequently formed have adoping of a first conductivity type, the lower source-level materiallayer 112 and the upper source-level semiconductor layer 116 have adoping of a second conductivity type that is the opposite of the firstconductivity type. The thickness of each of the lower source-levelmaterial layer 112 and the upper source-level semiconductor layer 116may be in a range from 10 nm to 300 nm, such as from 20 nm to 150 nm,although lesser and greater thicknesses may also be used.

The source-level sacrificial layer 104 includes a sacrificial materialthat may be removed selective to the lower sacrificial liner 103 and theupper sacrificial liner 105. In one embodiment, the source-levelsacrificial layer 104 may include a semiconductor material such asundoped amorphous silicon or a silicon-germanium alloy with an atomicconcentration of germanium greater than 20%. The thickness of thesource-level sacrificial layer 104 may be in a range from 30 nm to 400nm, such as from 60 nm to 200 nm, although lesser and greaterthicknesses may also be used.

The lower sacrificial liner 103 and the upper sacrificial liner 105include materials that may function as an etch stop material duringremoval of the source-level sacrificial layer 104. For example, thelower sacrificial liner 103 and the upper sacrificial liner 105 mayinclude silicon oxide, silicon nitride, and/or a dielectric metal oxide.In one embodiment, each of the lower sacrificial liner 103 and the uppersacrificial liner 105 may include a silicon oxide layer having athickness in a range from 2 nm to 30 nm, although lesser and greaterthicknesses may also be used.

The source-level insulating layer 117 includes a dielectric materialsuch as silicon oxide. The thickness of the source-level insulatinglayer 117 may be in a range from 20 nm to 400 nm, such as from 40 nm to200 nm, although lesser and greater thicknesses may also be used. Theoptional source-select-level conductive layer 118 may include aconductive material that may be used as a source-select-level gateelectrode. For example, the optional source-select-level conductivelayer 118 may include a doped semiconductor material such as dopedpolysilicon or doped amorphous silicon that may be subsequentlyconverted into doped polysilicon by an anneal process. The thickness ofthe optional source-select-level conductive layer 118 may be in a rangefrom 30 nm to 200 nm, such as from 60 nm to 100 nm, although lesser andgreater thicknesses may also be used.

The in-process source-level material layers 10′ may be formed directlyabove a subset of the semiconductor devices on the substrate 8 (e.g.,silicon wafer). As used herein, a first element is located “directlyabove” a second element if the first element is located above ahorizontal plane including a topmost surface of the second element andan area of the first element and an area of the second element has anareal overlap in a plan view (i.e., along a vertical plane or directionperpendicular to the top surface of the substrate 8.

The optional conductive plate layer 6 and the in-process source-levelmaterial layers 10′ may be patterned to provide openings in areas inwhich through-memory-level contact via structures, through-dielectriccontact via structures, and conductive via structures may besubsequently formed. Patterned portions of the stack of the conductiveplate layer 6 and the in-process source-level material layers 10′ may bepresent in each memory array region 100 in which three-dimensionalmemory stack structures are to be subsequently formed. The openingsthrough the optional conductive plate layer 6 and the in-processsource-level material layers 10′ may be formed within the memory arrayregion 100 in areas in which dielectric pillar structures are to besubsequently formed.

The optional conductive plate layer 6 and the in-process source-levelmaterial layers 10′ may be patterned such that an opening extends over astaircase region 200 in which contact via structures contacting wordline electrically conductive layers may be subsequently formed. In oneembodiment, the staircase region 200 may be laterally spaced from thememory array region 100 along a first horizontal direction hd1. Ahorizontal direction that is perpendicular to the first horizontaldirection hd1 is herein referred to as a second horizontal directionhd2. In one embodiment, additional openings in the optional conductiveplate layer 6 and the in-process source-level material layers 10′ may beformed within the area of a memory array region 100, in which athree-dimensional memory array including memory stack structures is tobe subsequently formed. A peripheral device region 400 that issubsequently filled with a field dielectric material portion may beprovided adjacent to the staircase region 200.

The region of the semiconductor devices 710 and the combination of thelower-level dielectric material layers 760 and the lower-level metalinterconnect structures 780 is herein referred to an underlyingperipheral device region 700, which is located underneath a memory-levelassembly to be subsequently formed and includes peripheral devices forthe memory-level assembly. The lower-level metal interconnect structures780 are formed within the lower-level dielectric material layers 760.

The lower-level metal interconnect structures 780 may be electricallyconnected to active nodes (e.g., transistor active regions 742 or gateelectrodes 754) of the semiconductor devices 710 (e.g., CMOS devices),and are located at the level of the lower-level dielectric materiallayers 760. Through-memory-level contact via structures may besubsequently formed directly on the lower-level metal interconnectstructures 780 to provide electrical connection to memory devices to besubsequently formed. In one embodiment, the pattern of the lower-levelmetal interconnect structures 780 may be selected such that thelanding-pad-level metal line structures 788 (which are a subset of thelower-level metal interconnect structures 780 located at the topmostportion of the lower-level metal interconnect structures 780) mayprovide landing pad structures for the through-memory-level conductivevia structures to be subsequently formed.

Referring to FIG. 2, an alternating stack of first material layers andsecond material layers may be subsequently formed. Each first materiallayer may include a first material, and each second material layer mayinclude a second material that is different from the first material. Inembodiments in which at least another alternating stack of materiallayers is subsequently formed over the alternating stack of the firstmaterial layers and the second material layers, the alternating stack isherein referred to as a first-tier alternating stack. The level of thefirst-tier alternating stack is herein referred to as a first-tierlevel, and the level of the alternating stack to be subsequently formedimmediately above the first-tier level is herein referred to as asecond-tier level, etc.

The first-tier alternating stack may include first insulting layers 132as the first material layers, and first spacer material layers as thesecond material layers. In one embodiment, the first spacer materiallayers may be sacrificial material layers that are subsequently replacedwith electrically conductive layers.

In one embodiment, the first material layers and the second materiallayers may be first insulating layers 132 and first sacrificial materiallayers 142, respectively. In one embodiment, each first insulating layer132 may include a first insulating material, and each first sacrificialmaterial layer 142 may include a first sacrificial material. Analternating plurality of first insulating layers 132 and firstsacrificial material layers 142 is formed over the in-processsource-level material layers 10′. As used herein, a “sacrificialmaterial” refers to a material that is removed during a subsequentprocessing step.

As used herein, an alternating stack of first elements and secondelements refers to a structure in which instances of the first elementsand instances of the second elements alternate. Each instance of thefirst elements that is not an end element of the alternating pluralityis adjoined by two instances of the second elements on both sides, andeach instance of the second elements that is not an end element of thealternating plurality is adjoined by two instances of the first elementson both ends. The first elements may have the same thickness throughout,or may have different thicknesses. The second elements may have the samethickness throughout, or may have different thicknesses. The alternatingplurality of first material layers and second material layers may beginwith an instance of the first material layers or with an instance of thesecond material layers, and may end with an instance of the firstmaterial layers or with an instance of the second material layers. Inone embodiment, an instance of the first elements and an instance of thesecond elements may form a unit that is repeated with periodicity withinthe alternating plurality.

The first-tier alternating stack (132, 142) may include first insulatinglayers 132 composed of the first material, and first sacrificialmaterial layers 142 composed of the second material, which is differentfrom the first material. The first material of the first insulatinglayers 132 may be at least one insulating material. Insulating materialsthat may be used for the first insulating layers 132 include, but arenot limited to silicon oxide (including doped or undoped silicateglass), silicon nitride, silicon oxynitride, organosilicate glass (OSG),spin-on dielectric materials, dielectric metal oxides that are commonlyknown as high dielectric constant (high-k) dielectric oxides (e.g.,aluminum oxide, hafnium oxide, etc.) and silicates thereof, dielectricmetal oxynitrides and silicates thereof, and organic insulatingmaterials. In one embodiment, the first material of the first insulatinglayers 132 may be silicon oxide.

The second material of the first sacrificial material layers 142 is asacrificial material that may be removed selective to the first materialof the first insulating layers 132. As used herein, a removal of a firstmaterial is “selective to” a second material if the removal processremoves the first material at a rate that is at least twice the rate ofremoval of the second material. The ratio of the rate of removal of thefirst material to the rate of removal of the second material is hereinreferred to as a “selectivity” of the removal process for the firstmaterial with respect to the second material.

The first sacrificial material layers 142 may comprise an insulatingmaterial, a semiconductor material, or a conductive material. The secondmaterial of the first sacrificial material layers 142 may besubsequently replaced with electrically conductive electrodes which mayfunction, for example, as control gate electrodes of a vertical NANDdevice. In one embodiment, the first sacrificial material layers 142 maybe material layers that comprise silicon nitride.

In one embodiment, the first insulating layers 132 may include siliconoxide, and sacrificial material layers may include silicon nitridesacrificial material layers. The first material of the first insulatinglayers 132 may be deposited, for example, by chemical vapor deposition(CVD). For example, if silicon oxide is used for the first insulatinglayers 132, tetraethylorthosilicate (TEOS) may be used as the precursormaterial for the CVD process. The second material of the firstsacrificial material layers 142 may be formed, for example, CVD oratomic layer deposition (ALD).

The thicknesses of the first insulating layers 132 and the firstsacrificial material layers 142 may be in a range from 20 nm to 50 nm,although lesser and greater thicknesses may be used for each firstinsulating layer 132 and for each first sacrificial material layer 142.The number of repetitions of the pairs of a first insulating layer 132and a first sacrificial material layer 142 may be in a range from 2 to1,024, and typically from 8 to 256, although a greater number ofrepetitions may also be used. In one embodiment, each first sacrificialmaterial layer 142 in the first-tier alternating stack (132, 142) mayhave a uniform thickness that is substantially invariant within eachrespective first sacrificial material layer 142.

A first insulating cap layer 170 is subsequently formed over thefirst-tier alternating stack (132, 142). The first insulating cap layer170 includes a dielectric material, which may be any dielectric materialthat may be used for the first insulating layers 132. In one embodiment,the first insulating cap layer 170 includes the same dielectric materialas the first insulating layers 132. The thickness of the firstinsulating cap layer 170 may be in a range from 20 nm to 300 nm,although lesser and greater thicknesses may also be used.

Referring to FIG. 3, the first insulating cap layer 170 and thefirst-tier alternating stack (132, 142) may be patterned to form firststepped surfaces in the staircase region 200. The staircase region 200may include a respective first stepped area in which the first steppedsurfaces are formed, and a second stepped area in which additionalstepped surfaces are to be subsequently formed in a second-tierstructure (to be subsequently formed over a first-tier structure) and/oradditional tier structures. The first stepped surfaces may be formed,for example, by forming a mask layer with an opening therein, etching acavity within the levels of the first insulating cap layer 170, anditeratively expanding the etched area and vertically recessing thecavity by etching each pair of a first insulating layer 132 and a firstsacrificial material layer 142 located directly underneath the bottomsurface of the etched cavity within the etched area. In one embodiment,top surfaces of the first sacrificial material layers 142 may bephysically exposed at the first stepped surfaces. The cavity overlyingthe first stepped surfaces is herein referred to as a first steppedcavity.

A dielectric fill material (such as undoped silicate glass or dopedsilicate glass) may be deposited to fill the first stepped cavity.Excess portions of the dielectric fill material may be removed fromabove the horizontal plane including the top surface of the firstinsulating cap layer 170. A remaining portion of the dielectric fillmaterial that fills the region overlying the first stepped surfacesconstitute a first retro-stepped dielectric material portion 165. Asused herein, a “retro-stepped” element refers to an element that hasstepped surfaces and a horizontal cross-sectional area that increasesmonotonically as a function of a vertical distance from a top surface ofa substrate on which the element is present. The first-tier alternatingstack (132, 142) and the first retro-stepped dielectric material portion165 collectively constitute a first-tier structure, which is anin-process structure that is subsequently modified.

An inter-tier dielectric layer 180 may be optionally deposited over thefirst-tier structure (132, 142, 170, 165). The inter-tier dielectriclayer 180 includes a dielectric material such as silicon oxide. In oneembodiment, the inter-tier dielectric layer 180 may include a dopedsilicate glass having a greater etch rate than the material of the firstinsulating layers 132 (which may include an undoped silicate glass). Forexample, the inter-tier dielectric layer 180 may include phosphosilicateglass. The thickness of the inter-tier dielectric layer 180 may be in arange from 30 nm to 300 nm, although lesser and greater thicknesses mayalso be used.

Referring to FIGS. 4A and 4B, various first-tier openings (149, 129) maybe formed through the inter-tier dielectric layer 180 and the first-tierstructure (132, 142, 170, 165) and into the in-process source-levelmaterial layers 10′. A photoresist layer (not shown) may be applied overthe inter-tier dielectric layer 180, and may be lithographicallypatterned to form various openings therethrough. The pattern of openingsin the photoresist layer may be transferred through the inter-tierdielectric layer 180 and the first-tier structure (132, 142, 170, 165)and into the in-process source-level material layers 10′ by a firstanisotropic etch process to form the various first-tier openings (149,129) concurrently, i.e., during the first isotropic etch process. Thevarious first-tier openings (149, 129) may include first-tier memoryopenings 149 and first-tier support openings 129. Locations of steps Sin the first-tier alternating stack (132, 142) are illustrated as dottedlines in FIG. 4B. The first-tier memory openings 149 may be openingsthat are formed in the memory array region 100 through each layer withinthe first-tier alternating stack (132, 142) and are subsequently used toform memory stack structures therein. The first-tier memory openings 149may be formed in clusters of first-tier memory openings 149 that arelaterally spaced apart along the second horizontal direction hd2. Eachcluster of first-tier memory openings 149 may be formed as atwo-dimensional array of first-tier memory openings 149.

The first-tier support openings 129 may be openings that are formed inthe staircase region 200 and are subsequently used to formstaircase-region contact via structures that interconnect a respectivepair of an underlying lower-level metal interconnect structure 780 (suchas a landing-pad-level metal line structure 788) and an electricallyconductive layer (which may be formed by replacement of a sacrificialmaterial layer within the electrically conductive layer). A subset ofthe first-tier support openings 129 that is formed through the firstretro-stepped dielectric material portion 165 may be formed through arespective horizontal surface of the first stepped surfaces. Further,each of the first-tier support openings 129 may be formed directly above(i.e., above, and with an areal overlap with) a respective one of thelower-level metal interconnect structure 780.

A subset of the first-tier support openings 129 may be formed insections of the memory array region 100 that are not filled with thefirst-tier memory openings 149. The sections of the memory array region100 that are not filled with the first-tier memory openings 149 may bedistributed over multiple areas within the memory array region 100.Discrete areas free of first-tier memory openings 149 and first-tiersupport openings 129 are provided in the memory array region 100.

In one embodiment, the first anisotropic etch process may include aninitial step in which the materials of the first-tier alternating stack(132, 142) are etched concurrently with the material of the firstretro-stepped dielectric material portion 165. The chemistry of theinitial etch step may alternate to optimize etching of the first andsecond materials in the first-tier alternating stack (132, 142) whileproviding a comparable average etch rate to the material of the firstretro-stepped dielectric material portion 165. The first anisotropicetch process may use, for example, a series of reactive ion etchprocesses or a single reaction etch process (e.g., CF₄/O₂/Ar etch). Thesidewalls of the various first-tier openings (149, 129) may besubstantially vertical, or may be tapered.

After etching through the alternating stack (132, 142) and the firstretro-stepped dielectric material portion 165, the chemistry of aterminal portion of the first anisotropic etch process may be selectedto etch through the dielectric material(s) of the at least one seconddielectric layer 768 with a higher etch rate than an average etch ratefor the in-process source-level material layers 10′. For example, theterminal portion of the anisotropic etch process may include a step thatetches the dielectric material(s) of the at least one second dielectriclayer 768 selective to a semiconductor material within a component layerin the in-process source-level material layers 10′. In one embodiment,the terminal portion of the first anisotropic etch process may etchthrough the source-select-level conductive layer 118, the source-levelinsulating layer 117, the upper source-level semiconductor layer 116,the upper sacrificial liner 105, the source-level sacrificial layer 104,and the lower sacrificial liner 103, and at least partly into the lowersource-level semiconductor layer 112. The terminal portion of the firstanisotropic etch process may include at least one etch chemistry foretching the various semiconductor materials of the in-processsource-level material layers 10′. The photoresist layer may besubsequently removed, for example, by ashing.

Optionally, the portions of the first-tier memory openings 149 and thefirst-tier support openings 129 at the level of the inter-tierdielectric layer 180 may be laterally expanded by an isotropic etch. Inthis case, the inter-tier dielectric layer 180 may comprise a dielectricmaterial (such as borosilicate glass) having a greater etch rate thanthe first insulating layers 132 (that may include undoped silicateglass) in dilute hydrofluoric acid. An isotropic etch (such as a wetetch using HF) may be used to expand the lateral dimensions of thefirst-tier memory openings 149 at the level of the inter-tier dielectriclayer 180. The portions of the first-tier memory openings 149 located atthe level of the inter-tier dielectric layer 180 may be optionallywidened to provide a larger landing pad for second-tier memory openingsto be subsequently formed through a second-tier alternating stack (to besubsequently formed prior to formation of the second-tier memoryopenings).

Referring to FIG. 5, sacrificial first-tier opening fill portions (148,128) may be formed in the various first-tier openings (149, 129). Forexample, a sacrificial first-tier fill material may be depositedconcurrently in each of the first-tier openings (149, 129). Thesacrificial first-tier fill material includes a material that may besubsequently removed selective to the materials of the first insulatinglayers 132 and the first sacrificial material layers 142.

In one embodiment, the sacrificial first-tier fill material may includea semiconductor material such as silicon (e.g., a-Si or polysilicon), asilicon-germanium alloy, germanium, a III-V compound semiconductormaterial, or a combination thereof. Optionally, a thin etch stop liner(such as a silicon oxide layer or a silicon nitride layer having athickness in a range from 1 nm to 3 nm) may be used prior to depositingthe sacrificial first-tier fill material. The sacrificial first-tierfill material may be formed by a non-conformal deposition or a conformaldeposition method.

In another embodiment, the sacrificial first-tier fill material mayinclude a silicon oxide material having a higher etch rate than thematerials of the first insulating layers 132, the first insulating caplayer 170, and the inter-tier dielectric layer 180. For example, thesacrificial first-tier fill material may include borosilicate glass orporous or non-porous organosilicate glass having an etch rate that is atleast 100 times higher than the etch rate of densified TEOS oxide (i.e.,a silicon oxide material formed by decomposition oftetraethylorthosilicate glass in a chemical vapor deposition process andsubsequently densified in an anneal process) in a 100:1 dilutehydrofluoric acid. In this case, a thin etch stop liner (such as asilicon nitride layer having a thickness in a range from 1 nm to 3 nm)may be used prior to depositing the sacrificial first-tier fillmaterial. The sacrificial first-tier fill material may be formed by anon-conformal deposition or a conformal deposition method.

In yet another embodiment, the sacrificial first-tier fill material mayinclude amorphous silicon or a carbon-containing material (such asamorphous carbon or diamond-like carbon) that may be subsequentlyremoved by ashing, or a silicon-based polymer that may be subsequentlyremoved selective to the materials of the first-tier alternating stack(132, 142).

Portions of the deposited sacrificial material may be removed from abovethe topmost layer of the first-tier alternating stack (132, 142), suchas from above the inter-tier dielectric layer 180. For example, thesacrificial first-tier fill material may be recessed to a top surface ofthe inter-tier dielectric layer 180 using a planarization process. Theplanarization process may include a recess etch, chemical mechanicalplanarization (CMP), or a combination thereof. The top surface of theinter-tier dielectric layer 180 may be used as an etch stop layer or aplanarization stop layer.

Remaining portions of the sacrificial first-tier fill material maycomprise sacrificial first-tier opening fill portions (148, 128).Specifically, each remaining portion of the sacrificial material in afirst-tier memory opening 149 may constitute a sacrificial first-tiermemory opening fill portion 148. Each remaining portion of thesacrificial material in a first-tier support opening 129 may constitutea sacrificial first-tier support opening fill portion 128. The varioussacrificial first-tier opening fill portions (148, 128) may beconcurrently formed, i.e., during a same set of processes including thedeposition process that deposits the sacrificial first-tier fillmaterial and the planarization process that removes the first-tierdeposition process from above the first-tier alternating stack (132,142) (such as from above the top surface of the inter-tier dielectriclayer 180). The top surfaces of the sacrificial first-tier opening fillportions (148, 128) may be coplanar with the top surface of theinter-tier dielectric layer 180. Each of the sacrificial first-tieropening fill portions (148, 128) may, or may not, include cavitiestherein.

Referring to FIG. 6, a second-tier structure may be formed over thefirst-tier structure (132, 142, 170, 148). The second-tier structure mayinclude an additional alternating stack of insulating layers and spacermaterial layers, which may be sacrificial material layers. For example,a second-tier alternating stack (232, 242) of material layers may besubsequently formed on the top surface of the first-tier alternatingstack (132, 142). The second-tier alternating stack (232, 242) includesan alternating plurality of third material layers and fourth materiallayers. Each third material layer may include a third material, and eachfourth material layer may include a fourth material that is differentfrom the third material. In one embodiment, the third material may bethe same as the first material of the first insulating layer 132, andthe fourth material may be the same as the second material of the firstsacrificial material layers 142.

In one embodiment, the third material layers may be second insulatinglayers 232 and the fourth material layers may be second spacer materiallayers that provide vertical spacing between each vertically neighboringpair of the second insulating layers 232. In one embodiment, the thirdmaterial layers and the fourth material layers may be second insulatinglayers 232 and second sacrificial material layers 242, respectively. Thethird material of the second insulating layers 232 may be at least oneinsulating material. The fourth material of the second sacrificialmaterial layers 242 may be a sacrificial material that may be removedselective to the third material of the second insulating layers 232. Thesecond sacrificial material layers 242 may comprise an insulatingmaterial, a semiconductor material, or a conductive material. The fourthmaterial of the second sacrificial material layers 242 may besubsequently replaced with electrically conductive electrodes which mayfunction, for example, as control gate electrodes of a vertical NANDdevice.

In one embodiment, each second insulating layer 232 may include a secondinsulating material, and each second sacrificial material layer 242 mayinclude a second sacrificial material. In this case, the second-tieralternating stack (232, 242) may include an alternating plurality ofsecond insulating layers 232 and second sacrificial material layers 242.The third material of the second insulating layers 232 may be deposited,for example, by chemical vapor deposition (CVD). The fourth material ofthe second sacrificial material layers 242 may be formed, for example,CVD or atomic layer deposition (ALD).

The third material of the second insulating layers 232 may be at leastone insulating material. Insulating materials that may be used for thesecond insulating layers 232 may be any material that may be used forthe first insulating layers 132. The fourth material of the secondsacrificial material layers 242 is a sacrificial material that may beremoved selective to the third material of the second insulating layers232. Sacrificial materials that may be used for the second sacrificialmaterial layers 242 may be any material that may be used for the firstsacrificial material layers 142. In one embodiment, the secondinsulating material may be the same as the first insulating material,and the second sacrificial material may be the same as the firstsacrificial material.

The thicknesses of the second insulating layers 232 and the secondsacrificial material layers 242 may be in a range from 20 nm to 50 nm,although lesser and greater thicknesses may be used for each secondinsulating layer 232 and for each second sacrificial material layer 242.The number of repetitions of the pairs of a second insulating layer 232and a second sacrificial material layer 242 may be in a range from 2 to1,024, and typically from 8 to 256, although a greater number ofrepetitions may also be used. In one embodiment, each second sacrificialmaterial layer 242 in the second-tier alternating stack (232, 242) mayhave a uniform thickness that is substantially invariant within eachrespective second sacrificial material layer 242.

Second stepped surfaces in the second stepped area may be formed in thestaircase region 200 using a same set of processing steps as theprocessing steps used to form the first stepped surfaces in the firststepped area with suitable adjustment to the pattern of at least onemasking layer. A second retro-stepped dielectric material portion 265may be formed over the second stepped surfaces in the staircase region200.

A second insulating cap layer 270 may be subsequently formed over thesecond-tier alternating stack (232, 242). The second insulating caplayer 270 includes a dielectric material that is different from thematerial of the second sacrificial material layers 242. In oneembodiment, the second insulating cap layer 270 may include siliconoxide. In one embodiment, the first and second sacrificial materiallayers (142, 242) may comprise silicon nitride.

Generally speaking, at least one alternating stack of insulating layers(132, 232) and spacer material layers (such as sacrificial materiallayers (142, 242)) may be formed over the in-process source-levelmaterial layers 10′, and at least one dielectric material portion (suchas the retro-stepped dielectric material portion (165, 265)) may beformed over the staircase regions on the at least one alternating stack(132, 142, 232, 242).

Optionally, drain-select-level isolation structures 72 may be formedthrough a subset of layers in an upper portion of the second-tieralternating stack (232, 242). The second sacrificial material layers 242that are cut by the drain-select-level isolation structures 72correspond to the levels in which drain-select-level electricallyconductive layers may be subsequently formed. The drain-select-levelisolation structures 72 may include a dielectric material such assilicon oxide. The drain-select-level isolation structures 72 maylaterally extend along a first horizontal direction hd1, and may belaterally spaced apart along a second horizontal direction hd2 that isperpendicular to the first horizontal direction hd1. The combination ofthe second-tier alternating stack (232, 242), the second retro-steppeddielectric material portion 265, the second insulating cap layer 270,and the optional drain-select-level isolation structures 72 collectivelyconstitute a second-tier structure (232, 242, 265, 270, 72).

Referring to FIGS. 7A and 7B, various second-tier openings (249, 229)may be formed through the second-tier structure (232, 242, 265, 270,72). A photoresist layer (not shown) may be applied over the secondinsulating cap layer 270, and may be lithographically patterned to formvarious openings therethrough. The pattern of the openings may be thesame as the pattern of the various first-tier openings (149, 129), whichis the same as the sacrificial first-tier opening fill portions (148,128). Thus, the lithographic mask used to pattern the first-tieropenings (149, 129) may be used to pattern the photoresist layer.

The pattern of openings in the photoresist layer may be transferredthrough the second-tier structure (232, 242, 265, 270, 72) by a secondanisotropic etch process to form various second-tier openings (249, 229)concurrently, i.e., during the second anisotropic etch process. Thevarious second-tier openings (249, 229) may include second-tier memoryopenings 249 and second-tier support openings 229.

The second-tier memory openings 249 may be formed directly on a topsurface of a respective one of the sacrificial first-tier memory openingfill portions 148. The second-tier support openings 229 may be formeddirectly on a top surface of a respective one of the sacrificialfirst-tier support opening fill portions 128. Further, each of thesecond-tier support openings 229 may be formed through a horizontalsurface within the second stepped surfaces, which include theinterfacial surfaces between the second-tier alternating stack (232,242) and the second retro-stepped dielectric material portion 265.Locations of steps S in the first-tier alternating stack (132, 142) andthe second-tier alternating stack (232, 242) are illustrated as dottedlines in FIG. 7B.

The second anisotropic etch process may include an etch step in whichthe materials of the second-tier alternating stack (232, 242) are etchedconcurrently with the material of the second retro-stepped dielectricmaterial portion 265. The chemistry of the etch step may alternate tooptimize etching of the materials in the second-tier alternating stack(232, 242) while providing a comparable average etch rate to thematerial of the second retro-stepped dielectric material portion 265.The second anisotropic etch process may use, for example, a series ofreactive ion etch processes or a single reaction etch process (e.g.,CF₄/O₂/Ar etch). The sidewalls of the various second-tier openings (249,229) may be substantially vertical, or may be tapered. A bottomperiphery of each second-tier opening (249, 229) may be laterallyoffset, and/or may be located entirely within, a periphery of a topsurface of an underlying sacrificial first-tier opening fill portion(148, 128). The photoresist layer may be subsequently removed, forexample, by ashing.

Referring to FIG. 8, the sacrificial first-tier fill material of thesacrificial first-tier opening fill portions (148, 128) may be removedusing an etch process that etches the sacrificial first-tier fillmaterial selective to the materials of the first and second insulatinglayers (132, 232), the first and second sacrificial material layers(142,242), the first and second insulating cap layers (170, 270), andthe inter-tier dielectric layer 180. A memory opening 49, which is alsoreferred to as an inter-tier memory opening 49, may be formed in eachcombination of a second-tier memory openings 249 and a volume from whicha sacrificial first-tier memory opening fill portion 148 is removed. Asupport opening 19, which is also referred to as an inter-tier supportopening 19, may be formed in each combination of a second-tier supportopenings 229 and a volume from which a sacrificial first-tier supportopening fill portion 128 is removed.

FIGS. 9A-9D provide sequential cross-sectional views of a memory opening49 during formation of a memory opening fill structure. The samestructural change occurs in each of the memory openings 49 and thesupport openings 19.

Referring to FIG. 9A, a memory opening 49 in the exemplary devicestructure of FIG. 8 is illustrated. The memory opening 49 extendsthrough the first-tier structure and the second-tier structure.

Referring to FIG. 9B, a stack of layers including a blocking dielectriclayer 52, a charge storage layer 54, a tunneling dielectric layer 56,and a semiconductor channel material layer 60L may be sequentiallydeposited in the memory openings 49. The blocking dielectric layer 52may include a single dielectric material layer or a stack of a pluralityof dielectric material layers. In one embodiment, the blockingdielectric layer may include a dielectric metal oxide layer consistingessentially of a dielectric metal oxide. As used herein, a dielectricmetal oxide refers to a dielectric material that includes at least onemetallic element and at least oxygen. The dielectric metal oxide mayconsist essentially of the at least one metallic element and oxygen, ormay consist essentially of the at least one metallic element, oxygen,and at least one non-metallic element such as nitrogen. In oneembodiment, the blocking dielectric layer 52 may include a dielectricmetal oxide having a dielectric constant greater than 7.9, i.e., havinga dielectric constant greater than the dielectric constant of siliconnitride. The thickness of the dielectric metal oxide layer may be in arange from 1 nm to 20 nm, although lesser and greater thicknesses mayalso be used. The dielectric metal oxide layer may subsequently functionas a dielectric material portion that blocks leakage of storedelectrical charges to control gate electrodes. In one embodiment, theblocking dielectric layer 52 includes aluminum oxide. Alternatively, oradditionally, the blocking dielectric layer 52 may include a dielectricsemiconductor compound such as silicon oxide, silicon oxynitride,silicon nitride, or a combination thereof.

Subsequently, the charge storage layer 54 may be formed. In oneembodiment, the charge storage layer 54 may be a continuous layer orpatterned discrete portions of a charge trapping material including adielectric charge trapping material, which may be, for example, siliconnitride. Alternatively, the charge storage layer 54 may include acontinuous layer or patterned discrete portions of a conductive materialsuch as doped polysilicon or a metallic material that is patterned intomultiple electrically isolated portions (e.g., floating gates), forexample, by being formed within lateral recesses into sacrificialmaterial layers (142, 242). In one embodiment, the charge storage layer54 includes a silicon nitride layer. In one embodiment, the sacrificialmaterial layers (142, 242) and the insulating layers (132, 232) may havevertically coincident sidewalls, and the charge storage layer 54 may beformed as a single continuous layer. Alternatively, the sacrificialmaterial layers (142, 242) may be laterally recessed with respect to thesidewalls of the insulating layers (132, 232), and a combination of adeposition process and an anisotropic etch process may be used to formthe charge storage layer 54 as a plurality of memory material portionsthat are vertically spaced apart. The thickness of the charge storagelayer 54 may be in a range from 2 nm to 20 nm, although lesser andgreater thicknesses may also be used.

The tunneling dielectric layer 56 includes a dielectric material throughwhich charge tunneling may be performed under suitable electrical biasconditions. The charge tunneling may be performed through hot-carrierinjection or by Fowler-Nordheim tunneling induced charge transferdepending on the mode of operation of the monolithic three-dimensionalNAND string memory device to be formed. The tunneling dielectric layer56 may include silicon oxide, silicon nitride, silicon oxynitride,dielectric metal oxides (such as aluminum oxide and hafnium oxide),dielectric metal oxynitride, dielectric metal silicates, alloys thereof,and/or combinations thereof. In one embodiment, the tunneling dielectriclayer 56 may include a stack of a first silicon oxide layer, a siliconoxynitride layer, and a second silicon oxide layer, which is commonlyknown as an ONO stack. In one embodiment, the tunneling dielectric layer56 may include a silicon oxide layer that is substantially free ofcarbon or a silicon oxynitride layer that is substantially free ofcarbon. The thickness of the tunneling dielectric layer 56 may be in arange from 2 nm to 20 nm, although lesser and greater thicknesses mayalso be used. The stack of the blocking dielectric layer 52, the chargestorage layer 54, and the tunneling dielectric layer 56 constitutes amemory film 50 that stores memory bits.

The semiconductor channel material layer 60L may include a dopedsemiconductor material such as at least one elemental semiconductormaterial, at least one III-V compound semiconductor material, at leastone II-VI compound semiconductor material, at least one organicsemiconductor material, or other semiconductor materials known in theart. The conductivity type of dopants in the semiconductor channelmaterial layer 60L is herein referred to as a first conductivity type,which may be p-type or n-type. In one embodiment, the semiconductorchannel material layer 60L has a p-type doping in which p-type dopants(such as boron atoms) are present at an atomic concentration in a rangefrom 1.0×10¹²/cm³ to 1.0×10¹⁸/cm³, such as from 1.0×10¹⁴/cm³ to1.0×10¹⁷/cm³. In one embodiment, the semiconductor channel materiallayer 60L includes, and/or consists essentially of, boron-dopedamorphous silicon or boron-doped polysilicon. In another embodiment, thesemiconductor channel material layer 60L has an n-type doping in whichn-type dopants (such as phosphor atoms or arsenic atoms) are present atan atomic concentration in a range from 1.0×10¹²/cm³ to 1.0×10¹⁸/cm³,such as from 1.0×10¹⁴/cm³ to 1.0×10¹⁷/cm³. The semiconductor channelmaterial layer 60L may be formed by a conformal deposition method suchas low pressure chemical vapor deposition (LPCVD). The thickness of thesemiconductor channel material layer 60L may be in a range from 2 nm to10 nm, although lesser and greater thicknesses may also be used. Acavity 49′ is formed in the volume of each memory opening 49 that is notfilled with the deposited material layers (52, 54, 56, 60L).

Referring to FIG. 9C, in case the cavity 49′ in each memory opening isnot completely filled by the semiconductor channel material layer 60L, adielectric core layer may be deposited in the cavity 49′ to fill anyremaining portion of the cavity 49′ within each memory opening. Thedielectric core layer includes a dielectric material such as siliconoxide or organosilicate glass. The dielectric core layer may bedeposited by a conformal deposition method such as low pressure chemicalvapor deposition (LPCVD), or by a self-planarizing deposition processsuch as spin coating. The horizontal portion of the dielectric corelayer overlying the second insulating cap layer 270 may be removed, forexample, by a recess etch. The recess etch continues until top surfacesof the remaining portions of the dielectric core layer are recessed to aheight between the top surface of the second insulating cap layer 270and the bottom surface of the second insulating cap layer 270. Eachremaining portion of the dielectric core layer constitutes a dielectriccore 62.

Referring to FIG. 9D, a doped semiconductor material may be deposited incavities overlying the dielectric cores 62. The doped semiconductormaterial has a doping of the opposite conductivity type of the doping ofthe semiconductor channel material layer 60L. In one embodiment, thedoped semiconductor material has an n-type doping. Portions of thedeposited doped semiconductor material, the semiconductor channelmaterial layer 60L, the tunneling dielectric layer 56, the chargestorage layer 54, and the blocking dielectric layer 52 that overlie thehorizontal plane including the top surface of the second insulating caplayer 270 may be removed by a planarization process such as a chemicalmechanical planarization (CMP) process.

Each remaining portion of the doped semiconductor material—constitutes adrain region 63. The dopant concentration in the drain regions 63 may bein a range from 5.0×10¹⁹/cm³ to 2.0×10²¹/cm³, although lesser andgreater dopant concentrations may also be used. The doped semiconductormaterial may be, for example, doped polysilicon.

Each remaining portion of the semiconductor channel material layer 60Lconstitutes a vertical semiconductor channel 60 through which electricalcurrent may flow when a vertical NAND device including the verticalsemiconductor channel 60 is turned on. A tunneling dielectric layer 56may be surrounded by a charge storage layer 54, and laterally surroundsa vertical semiconductor channel 60. Each adjoining set of a blockingdielectric layer 52, a charge storage layer 54, and a tunnelingdielectric layer 56 collectively constitute a memory film 50, which maystore electrical charges with a macroscopic retention time. In someembodiments, a blocking dielectric layer 52 is be present in the memoryfilm 50 at this step, and a backside blocking dielectric layer may besubsequently formed after formation of backside recesses. As usedherein, a macroscopic retention time refers to a retention time suitablefor operation of a memory device as a permanent memory device such as aretention time in excess of 24 hours.

Each combination of a memory film 50 and a vertical semiconductorchannel 60 (which is a vertical semiconductor channel) within a memoryopening 49 may constitute a memory stack structure 55. The memory stackstructure 55 is a combination of a vertical semiconductor channel 60, atunneling dielectric layer 56, a plurality of memory elements comprisingportions of the charge storage layer 54, and an optional blockingdielectric layer 52. Each combination of a memory stack structure 55, adielectric core 62, and a drain region 63 within a memory opening 49 mayconstitute a memory opening fill structure 58. Each drain region 63 in amemory opening fill structure 58 is electrically connected to an upperend of a respective one of the vertical semiconductor channels 60. Thein-process source-level material layers 10′, the first-tier structure(132, 142, 170, 165), the second-tier structure (232, 242, 270, 265,72), the inter-tier dielectric layer 180, and the memory opening fillstructures 58 collectively constitute a memory-level assembly.

Referring to FIG. 10, the exemplary structure is illustrated afterformation of the memory opening fill structures 58. Support pillarstructures 20 are formed in the support openings 19 concurrently withformation of the memory opening fill structures 58. Each support pillarstructure 20 may have a same set of components as a memory opening fillstructure 58. Each of the alternating stacks {(132, 142), (232, 242)}comprises a terrace region (i.e., the staircase region 200) in whicheach sacrificial material layer (142, 242) other than a topmostsacrificial material layer (142, 242) within the alternating stack{(132, 142) and/or (232, 242)} laterally extends farther than anyoverlying sacrificial material layer (142, 242) within the alternatingstack {(132, 142) and/or (232, 242)}. The terrace region includesstepped surfaces of the alternating stack that continuously extend froma bottommost layer within the alternating stack {(132, 142) or (232,242)} to a topmost layer within the alternating stack {(132, 142) or(232, 242)}. Support pillar structures 20 extend through the steppedsurfaces and through a retro-stepped dielectric material portion (165 or265) that overlies the stepped surfaces.

Referring to FIGS. 11A-11E, a first contact level dielectric layer 280may be formed over the second-tier structure (232, 242, 270, 265, 72).The first contact level dielectric layer 280 includes a dielectricmaterial such as silicon oxide, and may be formed by a conformal ornon-conformal deposition process. For example, the first contact leveldielectric layer 280 may include undoped silicate glass and may have athickness in a range from 100 nm to 600 nm, although lesser and greaterthicknesses may also be used.

A photoresist layer (not shown) may be applied over the first contactlevel dielectric layer 280, and may be lithographically patterned toform various openings in the memory array region 100 and the staircaseregion 200. The openings in the photoresist layer may include elongatedopenings that laterally extend along the first horizontal direction hd1across the memory array region 100 and the staircase region 200 betweenclusters of memory opening fill structures 58 and support pillarstructures 20, and sets of nested openings located between neighboringpairs of elongated openings. As used herein, “nested openings” refer toopenings that are laterally surrounded by, or laterally surrounding,each other opening. Each of the nested openings on the photoresist layermay be located within areas of the memory array region 100 that are freeof the memory opening fill structures 58.

An anisotropic etch may be performed to transfer the pattern in thephotoresist layer through underlying material portions including thealternating stacks {(132, 142), (232, 242)}, the retro-steppeddielectric material portions (165, 265), an upper portion of thein-process source-level material layers 10′, and the at least one seconddielectric layer 768. Backside trenches 79 may be formed underneath theelongated openings in the photoresist layer through the first contactlevel dielectric layer 280, the second-tier structure (232, 242, 270,265, 72), and the first-tier structure (132, 142, 170, 165), and intothe in-process source-level material layers 10′. Portions of the firstcontact level dielectric layer 280, the second-tier structure (232, 242,270, 265, 72), the first-tier structure (132, 142, 170, 165), and thein-process source-level material layers 10′ that underlie the openingsin the photoresist layer may be removed to form the backside trenches79. In one embodiment, the backside trenches 79 may be formed betweenclusters of memory stack structures 55. The clusters of the memory stackstructures 55 may be laterally spaced apart along the second horizontaldirection hd2 by the backside trenches 79. A top surface of asource-level sacrificial layer 104 may be physically exposed at thebottom of each backside trench 79.

The anisotropic etch may form sets of nested trenches (179, 279) bytransferring the pattern of the sets of nested openings in thephotoresist layer to underlying material portions. As used herein,“nested trenches” refer to trenches that are laterally surrounded by, orlaterally surrounding, each other trench. Thus, each trench within a setof nested trenches (179, 279) may be laterally surrounded by, orlaterally surrounds, each other trench in the set of nested trenches.The sets of nested trenches (179, 279) extend through the first contactlevel dielectric layer 280, the second-tier structure (232, 242, 270,265, 72), and the first-tier structure (132, 142, 170, 165) and intoupper regions of at least one second dielectric layer 768 located withinopenings in the in-process source-level material layers 10′.

Each set of nested trenches (179, 279) includes an outer trench 279 andat least one inner trench 179 that is laterally surrounded at least bythe outer trench 279. Each outer trench 279 may be a moat trench, i.e.,a trench having a horizontal cross-sectional shape of a moat (i.e., alaterally enclosing band-shaped area that encircles an enclosed areatherein). The at least one inner trench 179 of each set of nestedtrenches (179, 279) may include a single inner trench 179 or a pluralityof inner trenches 179. In embodiments in which the at least one innertrench 179 of each set of nested trenches (179, 279) includes aplurality of inner trenches 179, at least one of the inner trenches 179may be a moat trench. Every inner trench 179 within each set of nestedtrenches (179, 279) may be a moat trench, or one inner trench 179 withineach set of nested trenches (179, 279) may include a cylindrical trenchhaving a horizontal cross-sectional shape of a two-dimensional shapewithout an opening therethrough. In one embodiment, each set of nestedtrenches (179, 279) may cut through at least drain-select-levelisolation structure 72 located between a neighboring pair of backsidetrenches 79. A sidewall of at least one drain-select-level isolationstructure 72 may be physically exposed on an outer sidewall of an outertrench 279.

Each remaining portion of the first insulating layers 132 inside anouter trench 279 is herein referred to as a first insulating plate 132′,and each remaining portion of the second insulating layers 232 inside anouter trench 279 is herein referred to as a second insulating plate232′. Each remaining portion of the first sacrificial material layers142 within inside an outer trench 279 is herein referred to as a firstsacrificial material plate 142′, and each remaining portion of thesecond sacrificial material layers 242 within inside an outer trench 279is herein referred to as a second sacrificial material plate 242′. Atleast one vertically alternating sequence of insulating plates (132′and/or 232′) and sacrificial material plates (142′ and/or 242′) isformed within each outer trench 279. Each vertically alternatingsequence of insulating plates (132′, 232′) and sacrificial materialplates (142′, 242′) includes a set of remaining material portions of thefirst contact level dielectric layer 280, the second-tier structure(232, 242, 270, 265, 72), and the first-tier structure (132, 142, 170,165).

Each of the insulating plates (132′, 232′) may be located at a samevertical distance as a respective one of the insulating layers (132,232) in the alternating stack {(132, 142) and/or (232, 242)} from a topsurface of the substrate 8. In one embodiment, the insulating plates(132′, 232′) and the insulating layers (132, 232) have a same materialcomposition. In one embodiment, the sacrificial material plates (142′,242′) comprise silicon nitride, and the insulating plates (132′, 232′)comprise silicon oxide such as an undoped silicate glass or a dopedsilicate glass. A drain-select-level isolation structure 72 may beformed within an upper region of the second-tier alternating stack (232,242), and may vertically extend through, and laterally divide, at leasta topmost one of the second sacrificial material layers 242. A sidewallof the drain-select-level isolation structure 72 may be physicallyexposed to an outer trench 279.

Generally, the backside trenches 79 and sets of nested trenches (179,279) may be simultaneously formed through the alternating stack {(132,142), (232, 242)} around the memory stack structures 55. Each trenchwithin the set of nested trenches (179, 279) may be spaced from anyother trench within the set of nested trenches (179, 279) by at leastone patterned remaining portion of the alternating stack {(132, 142),(232, 242)} having a respective shape of an enclosing wall. As usedherein, an “enclosing wall” refers to a vertically extending structurethat encircles, and encloses, a volume therein. As such, each “enclosingwall” has a horizontal cross-sectional shape that is topologicallyhomeomorphic to an annulus and is invariant, or changes only gradually,under translation along a vertical direction. The backside trenches 79may laterally extends along the first horizontal direction hd1, and maybe laterally spaced from each other along the second horizontaldirection hd2.

In one embodiment, each set of nested trenches (179, 279) may be formedbetween a respective neighboring pair of backside trenches 79. As usedherein, a “neighboring pair” of elements refers to two elements withinany intervening element within a volume between the two elements. In oneembodiment, each set of nested trenches (179, 279) may be formed withinan area of an opening through the in-process source-level materiallayers 10′.

In one embodiment, each of backside trenches 79 and each nested trenchwithin the sets of nested trenches (179, 279) may be formed withsidewalls having a bowing profile that provides a width at a heightbetween a topmost layer of the alternating stack {(132, 146), (232,246)} and a bottommost layer of the alternating stack {(132, 146), (232,246)} that is greater than a width at a height of the topmost layer ofthe alternating stack {(132, 146), (232, 246)}, and is greater than awidth at a height of the bottommost layer of the alternating stack{(132, 146), (232, 246)}. The bowing profile of the each of backsidetrenches 79 and each nested trench within the sets of nested trenches(179, 279) is due to the chemistry of the anisotropic etch process thatcauses gradual widening of regions that are not masked by the patternedphotoresist layer. Portions of the alternating stack {(132, 146), (232,246)} that are proximal to the patterned photoresist layer are masked bythe photoresist layer. Portions of the alternating stack {(132, 146),(232, 246)} that are proximal to the bottommost layer of the alternatingstack {(132, 146), (232, 246)} are exposed to etch gases only during theterminal portion of the anisotropic etch process. Middle portions of thealternating stack {(132, 146), (232, 246)} are not sufficiently maskedby the patterned photoresist layer and may be exposed to the etch gasesfor a significant duration of time, thereby developing the bowingprofiles illustrated in FIGS. 11A and 11B. The ratio of the maximumwidth of each backside trench 79 to the width of the backside trench 79at a topmost portion (i.e., at the interface between the firstcontact-level dielectric material layer 280 and the photoresist layer)may be in a range from 1.05 to 2.0, although lesser and greater ratiosmay also be used. The patterned photoresist layer may be subsequentlyremoved, for example, by ashing.

Referring to FIGS. 12A-12C, a sacrificial fill material may be depositedin the backside trenches 79 and the sets of nested trenches (179, 279).The sacrificial fill material includes a material that may be removedselective to the materials of the insulating layers (132, 232), thesacrificial material layers (142, 242), and the first contact leveldielectric layer 280. For example, the sacrificial fill material mayinclude amorphous silicon, a silicon-germanium alloy, amorphous carbon,porous or non-porous organosilicate glass, or an organic or non-organicpolymer material. In one embodiment, the sacrificial fill material mayinclude amorphous silicon. Excess portions of the sacrificial fillmaterial may be removed from above the horizontal plane including thetop surface of the first contact level dielectric layer 280.

Each remaining portion of the sacrificial fill material that fills abackside trench 79 is herein referred to as a sacrificial backsidetrench fill material structure 77. Each remaining portion of thesacrificial fill material that fills an outer trench 279 is hereinreferred to as a sacrificial outer trench fill structure 277. Eachremaining portion of the sacrificial fill material that fills an innertrench 179 is herein referred to as a sacrificial inner trench fillstructure 177. Sets of sacrificial nested trench fill structures (177,277) may be formed between a respective neighboring pair of sacrificialbackside trench fill material structures 77. Each set of sacrificialnested trench fill structures (177, 277) includes a sacrificial outertrench fill structure 277 and at least one sacrificial inner trench fillstructure 177. Support pillar structures 20 may be present between a setof sacrificial nested trench fill structures (177, 277) and aneighboring one of the sacrificial backside trench fill materialstructures 77.

Each set of sacrificial nested trench fill structures (177, 277) may beformed within the volume of a respective set of nested trenches (179,279) concurrently with formation of sacrificial backside trench fillmaterial structures 77. The sacrificial outer trench fill structures277, the sacrificial inner trench fill structures 177, and thesacrificial backside trench fill material structures 77 may include asame sacrificial fill material. In one embodiment, the sacrificialmaterial layers (142, 242) comprise silicon nitride, and the sets ofsacrificial nested trench fill structures (177, 277) comprise asemiconductor material or a carbon-based material.

Referring to FIGS. 13A-13C, a patterned etch mask layer 167 may beformed over the first contact level dielectric layer 280. The patternedetch mask layer 167 may be an insulating material layer or a photoresistmaterial layer that is lithographically patterned to form openings 168.For example, the patterned etch mask layer 167 may be hard mask, such asan aluminum oxide layer or silicon oxide layer that is lithographicallypatterned using an overlying photoresist layer (not shown for clarity).The pattern of the openings 168 may be selected such the entireperiphery of each opening 168 overlies a respective one of thevertically alternating sequences of insulating plates (132′, 232′) andsacrificial material plates (142′, 242′). In one embodiment, the entireperiphery of each opening in the patterned etch mask layer 167 may belocated between an outer periphery of a patterned remaining portion ofthe first contact-level dielectric material layer 280 contacting aninner sidewall of a respective sacrificial outer trench fill structure277. The entire top surface of each sacrificial inner trench fillstructure 177 may be physically exposed under the openings in thepatterned etch mask layer 167. The patterned etch mask layer 167 coversthe entire areas of the sacrificial outer trench fill structures 277 andthe sacrificial backside trench fill material structures 77.

Thus, a sacrificial inner trench fill structure 177 of each set ofsacrificial nested trench fill structures (177, 277) is physicallyexposed under the openings 168 in the patterned etch mask layer 167. Asacrificial outer trench fill structure 277 of each set of sacrificialnested trench fill structures (177, 277) (which laterally surrounds theat least one sacrificial inner trench fill structure 177 of the set ofsacrificial nested trench fill structures (177, 277) is covered by thepatterned etch mask layer 167.

Referring to FIGS. 14A-14C, an etch process may be performed to removethe sacrificial inner trench fill structures 177 exposed in the openings168 selective to the materials of the vertically alternating sequencesof insulating plates (132′, 232′) and sacrificial material plates (142′,242′), the first contact-level dielectric material layer 280, and the atleast one second dielectric layer 768. The at least one sacrificialinner trench fill structure 177 of each set of sacrificial nested trenchfill structures (177, 277) may be removed selective to the patternedremaining portions of the alternating stack {(132, 142), (232, 242)},i.e., selective to the vertically alternating sequences of insulatingplates (132′, 232′) and sacrificial material plates (142′, 242′). A voidmay be formed in each volume from which a sacrificial inner trench fillstructure 177 is removed through a respective opening 168 in thepatterned etch mask layer 167.

Removal of the sacrificial inner trench fill structures 177 of the setsof sacrificial nested trench fill structures (177, 277) may be performedselective to materials of the insulating layers (132, 232) and thesacrificial material layers using an anisotropic etch process or anisotropic etch process. If the sacrificial inner trench fill structures177 include amorphous silicon, a wet etch process using hot trimethyl-2hydroxyethyl ammonium hydroxide (“hot TMY”) or tetramethyl ammoniumhydroxide (TMAH) may be used to remove the sacrificial inner trench fillstructures 177. Once the sacrificial inner trench fill structures 177are removed, the volumes of the inner trenches 179 become voids, i.e.,become cavities. Each void of the inner trenches 179 may be laterallybounded by at least one vertically alternating sequences of insulatingplates (132′, 232′) and sacrificial material plates (142′, 242′).

Referring to FIGS. 15A-15D, patterned remaining portions of thealternating stack {(132, 142), (232, 242)}, i.e., the verticallyalternating sequences of insulating plates (132′, 232′) and sacrificialmaterial plates (142′, 242′), that are exposed in the openings 168 inthe patterned etch mask layer 167 may be removed using a first isotropicetch process selective to the sacrificial outer trench fill structures277. At least one isotropic etchant is applied to the verticallyalternating sequences of insulating plates (132′, 232′) and sacrificialmaterial plates (142′, 242′) through the voids of the inner trenches179. Each vertically alternating sequence of insulating plates (132′,232′) and sacrificial material plates (142′, 242′) laterally surroundedby a sacrificial outer trench fill structure 277 is physically exposedto at least one inner trench 179. The isotropic etchant(s) and theduration of the first isotropic etch process may be selected such thatthe entirety of each vertically alternating sequence of insulatingplates (132′, 232′) and sacrificial material plates (142′, 242′) isremoved by the first isotropic etch process. In one embodiment, theinsulating plates (132′, 232′) may include silicon oxide and sacrificialmaterial plates (142′, 242′) may include silicon nitride. In this case,the first isotropic etch process may use sequential application ofphosphoric acid and hydrofluoric acid, or application of a mixture ofphosphoric acid and hydrofluoric acid. Access of the at least oneisotropic etchant to the backside trenches 79 (which are filled with thesacrificial backside trench fill material structures 77) may beprevented by the patterned etch mask layer 167. If the patterned etchmask layer 167 comprises silicon oxide, then it may comprise a siliconoxide material having a different composition (e.g., boron and/orphosphorus doped silicon oxide versus undoped silicon oxide) ordifferent density (e.g., formed by a different deposition method and/orusing a different precursor) than the silicon oxide material of theinsulating plates (132′, 232′). A pillar-shaped cavity 379 may be formedwithin each volume that is laterally enclosed by a sacrificial outertrench fill structure 277 and exposed in the respective opening 168 inthe patterned etch mask layer 167.

Referring to FIGS. 16A-16C, the sacrificial outer trench fill structures277 may be removed selective to the alternating stacks {(132, 146),(232, 246)} using a second isotropic or anisotropic etch process. Thesecond etch process removes the material of the sacrificial outer trenchfill structures 277 selective to materials of the insulating layers(132, 232) and the sacrificial material layers (142, 242). If thesacrificial outer trench fill structures 277 include amorphous silicon,a wet etch process using hot trimethyl-2 hydroxyethyl ammonium hydroxide(“hot TMY”) or tetramethyl ammonium hydroxide (TMAH) may be used toremove the sacrificial outer trench fill structures 277. Once thesacrificial outer trench fill structures 277 are removed, eachpillar-shaped cavity 379 expands by the volume from which a neighboringone of the sacrificial outer trench fill structures 277 is removed. Eachpillar-shaped cavity 379 may include a void that is located under arespective opening 168 in the patterned etch mask layer 167 and that islaterally bounded by a respective alternating stack {(132, 142), (232,242)} of insulating layers (132, 232) and sacrificial material layers(142, 242). The patterned etch mask layer 167 may be removed, forexample, by ashing if it comprises photoresist, or by selective etchingif it comprises an insulating material.

Generally, each set of sacrificial nested trench fill structures (177,277) may be sequentially removed while sacrificial backside trench fillmaterial structures 77 fill the backside trenches 79 and the patternedetch mask layer covers all alternating stacks {(132, 142), (232, 2342)}of insulating layers (132, 232) and sacrificial material layers (142,232) and all of the sacrificial backside trench fill material structures77.

Referring to FIGS. 17A-17C, a dielectric material having a differentmaterial composition than the sacrificial material layers (142, 242) maybe deposited in the pillar-shaped cavities 379. For example, a silicateglass material (such as undoped silicate glass or a doped silicateglass) and/or a dielectric metal oxide material may be deposited in thepillar-shaped cavities 379. Excess portions of the dielectric materialmay be removed from above the horizontal plane including the top surfaceof the first contact level dielectric layer 280 by a planarizationprocess, which may include chemical mechanical planarization (CMP) or arecess etch. Each remaining portion of the deposited dielectric materialin the pillar-shaped cavities 379 constitutes a dielectric pillarstructure 374. Each dielectric pillar structure 374 may have straightsidewalls that extend from the at least one second dielectric layer 768within an opening in the in-process source-level material layers 10′,and may have a respective horizontal cross-sectional area that isinvariant under translation along the vertical direction. Eachdielectric pillar structure 374 vertically extends through eachinsulating layer (132, 232) and each sacrificial material layer (142,242) within a respective alternating stack {(132, 142), (232, 242)} ofinsulating layers (132, 232) and sacrificial material layers (142, 242).In one embodiment, a drain-select-level isolation structure 72 formedwithin an upper region of the alternating stack {(132, 142), (232, 242)}may contact an outer sidewall of the dielectric pillar structure 374.

Referring to FIG. 18, an etch process may be performed to remove thesacrificial backside trench fill material structures 77 selective to thematerials of the first contact-level dielectric material layer 280, theinsulating layers (132, 232), the sacrificial material layers (142,242), and the dielectric pillar structures 374. If the sacrificialbackside trench fill material structures 77 include amorphous silicon, awet etch process using hot trimethyl-2 hydroxyethyl ammonium hydroxide(“hot TMY”) or tetramethyl ammonium hydroxide (TMAH) may be used toremove the sacrificial outer trench fill structures 277. Voids areformed in the volumes of the backside trenches 79 upon removal of thesacrificial backside trench fill material structures 77. The etchprocess may be performed without any patterned mask layer (such as apatterned photoresist layer).

Referring to FIG. 19A, a backside trench spacer 74 may be formed onsidewalls of each backside trench 79. For example, a conformal spacermaterial layer may be deposited in the backside trenches 79 and over thefirst contact level dielectric layer 280, and may be anisotropicallyetched to form the backside trench spacers 74. The backside trenchspacers 74 include a material that is different from the material of thesource-level sacrificial layer 104. For example, the backside trenchspacers 74 may include silicon nitride.

Referring to FIG. 19B, an etchant that etches the material of thesource-level sacrificial layer 104 selective to the materials of thefirst-tier alternating stack (132, 142), the second-tier alternatingstack (232, 242), the first and second insulating cap layers (170, 270),the first contact level dielectric layer 280, the upper sacrificialliner 105, and the lower sacrificial liner 103 may be introduced intothe backside trenches in an isotropic etch process. For example, if thesource-level sacrificial layer 104 includes undoped amorphous silicon oran undoped amorphous silicon-germanium alloy, the backside trenchspacers 74 include silicon nitride, and the upper and lower sacrificialliners (105, 103) include silicon oxide, a wet etch process using hottrimethyl-2 hydroxyethyl ammonium hydroxide (“hot TMY”) or tetramethylammonium hydroxide (TMAH) may be used to remove the source-levelsacrificial layer 104 selective to the backside trench spacers 74 andthe upper and lower sacrificial liners (105, 103). A source cavity 109is formed in the volume from which the source-level sacrificial layer104 is removed.

Wet etch chemicals such as hot TMY and TMAH are selective to the dopedsemiconductor materials of the upper source-level semiconductor layer116 and the lower source-level semiconductor layer 112. Thus, use ofselective wet etch chemicals such as hot TMY and TMAH for the wet etchprocess that forms the source cavity 109 may provide a large processwindow against etch depth variation during formation of the backsidetrenches 79. Specifically, even if sidewalls of the upper source-levelsemiconductor layer 116 are physically exposed or even if a surface ofthe lower source-level semiconductor layer 112 is physically exposedupon formation of the source cavity 109 and/or the backside trenchspacers 74, collateral etching of the upper source-level semiconductorlayer 116 and/or the lower source-level semiconductor layer 112 isminimal, and the structural change to the exemplary structure caused byaccidental physical exposure of the surfaces of the upper source-levelsemiconductor layer 116 and/or the lower source-level semiconductorlayer 112 during manufacturing steps do not result in device failures.Each of the memory opening fill structures 58 is physically exposed tothe source cavity 109. Specifically, each of the memory opening fillstructures 58 includes a sidewall and a bottom surface that arephysically exposed to the source cavity 109.

Referring to FIG. 19C, a sequence of isotropic etchants, such as wetetchants, may be applied to the physically exposed portions of thememory films 50 to sequentially etch the various component layers of thememory films 50 from outside to inside, and to physically exposecylindrical surfaces of the vertical semiconductor channels 60 at thelevel of the source cavity 109. The upper and lower sacrificial liners(105, 103) may be collaterally etched during removal of the portions ofthe memory films 50 located at the level of the source cavity 109. Thesource cavity 109 may be expanded in volume by removal of the portionsof the memory films 50 at the level of the source cavity 109 and theupper and lower sacrificial liners (105, 103). A top surface of thelower source-level semiconductor layer 112 and a bottom surface of theupper source-level semiconductor layer 116 may be physically exposed tothe source cavity 109. The source cavity 109 is formed by isotropicallyetching the source-level sacrificial layer 104 and a bottom portion ofeach of the memory films 50 selective to at least one source-levelsemiconductor layer (such as the lower source-level semiconductor layer112 and the upper source-level semiconductor layer 116) and the verticalsemiconductor channels 60.

Referring to FIG. 19D, a doped semiconductor material having a doping ofthe second conductivity type may be deposited on the physically exposedsemiconductor surfaces around the source cavity 109. The secondconductivity type is the opposite of the first conductivity type, whichis the conductivity type of the doping of the vertical semiconductorchannels 60. The physically exposed semiconductor surfaces includebottom portions of outer sidewalls of the vertical semiconductorchannels 60 and horizontal surfaces of the at least one source-levelsemiconductor layer (112, 116). For example, the physically exposedsemiconductor surfaces may include the bottom portions of outersidewalls of the vertical semiconductor channels 60, the top horizontalsurface of the lower source-level semiconductor layer 112, and thebottom surface of the upper source-level semiconductor layer 116.

In one embodiment, the doped semiconductor material of the secondconductivity type may be deposited on the physically exposedsemiconductor surfaces around the source cavity 109 by a selectivesemiconductor deposition process. A semiconductor precursor gas, anetchant, and an n-type dopant precursor gas may be flowed concurrentlyinto a process chamber including the exemplary structure during theselective semiconductor deposition process. For example, thesemiconductor precursor gas may include silane, disilane, ordichlorosilane, the etchant gas may include gaseous hydrogen chloride,and the n-type dopant precursor gas such as phosphine, arsine, orstibine. In this case, the selective semiconductor deposition processgrows an in-situ doped semiconductor material from physically exposedsemiconductor surfaces around the source cavity 109. The deposited dopedsemiconductor material forms a source contact layer 114, which maycontact sidewalls of the vertical semiconductor channels 60. The atomicconcentration of the dopants of the second conductivity type in thedeposited semiconductor material may be in a range from 1.0×10²⁰/cm³ to2.0×10²¹/cm³, such as from 2.0×10²⁰/cm³ to 8.0×10²⁰/cm³. The sourcecontact layer 114 as initially formed may consist essentially ofsemiconductor atoms and the dopant atoms of the second conductivitytype. Alternatively, at least one non-selective doped semiconductormaterial deposition process may be used to form the source contact layer114. Optionally, one or more etch back processes may be used incombination with a plurality of selective or non-selective depositionprocesses to provide a seamless and/or voidless source contact layer114.

The duration of the selective semiconductor deposition process may beselected such that the source cavity 109 is filled with the sourcecontact layer 114, and the source contact layer 114 contacts bottom endportions of inner sidewalls of the backside trench spacers 74. In oneembodiment, the source contact layer 114 may be formed by selectivelydepositing a doped semiconductor material from semiconductor surfacesaround the source cavity 109. In one embodiment, the doped semiconductormaterial may include doped polysilicon. Thus, the source-levelsacrificial layer 104 may be replaced with the source contact layer 114.

The layer stack including the lower source-level semiconductor layer112, the source contact layer 114, and the upper source-levelsemiconductor layer 116 constitutes a source region (112, 114, 116). Thesource region (112, 114, 116) is electrically connected to a first end(such as a bottom end) of each of the vertical semiconductor channels60. The set of layers including the source region (112, 114, 116), thesource-level insulating layer 117, and the source-select-levelconductive layer 118 constitutes source-level material layers 10, whichreplaces the in-process source-level material layers 10′.

Referring to FIGS. 19E and 20, the backside trench spacers 74 may beremoved selective to the insulating layers (132, 232), the first andsecond insulating cap layers (170, 270), the first contact leveldielectric layer 280, and the source contact layer 114 using anisotropic etch process. For example, if the backside trench spacers 74include silicon nitride, a wet etch process using hot phosphoric acidmay be performed to remove the backside trench spacers 74. In oneembodiment, the isotropic etch process that removes the backside trenchspacers 74 may be combined with a subsequent isotropic etch process thatetches the sacrificial material layers (142, 242) selective to theinsulating layers (132, 232), the first and second insulating cap layers(170, 270), the first contact level dielectric layer 280, and the sourcecontact layer 114.

An oxidation process may be performed to convert physically exposedsurface portions of semiconductor materials into dielectricsemiconductor oxide portions. For example, surfaces portions of thesource contact layer 114 and the upper source-level semiconductor layer116 may be converted into dielectric semiconductor oxide plates 122, andsurface portions of the source-select-level conductive layer 118 may beconverted into annular dielectric semiconductor oxide spacers 124. Thedielectric semiconductor oxide plates 122 and the annular dielectricsemiconductor oxide spacers 124 are omitted in FIG. 20 for clarity.

Referring to FIG. 21, the sacrificial material layers (142, 242) are maybe removed selective to the insulating layers (132, 232), the first andsecond insulating cap layers (170, 270), the first contact leveldielectric layer 280, the source contact layer 114, the dielectricsemiconductor oxide plates 122, the annular dielectric semiconductoroxide spacers 124, and the dielectric pillar structures 374. Forexample, an etchant that selectively etches the materials of thesacrificial material layers (142, 242) with respect to the materials ofthe insulating layers (132, 232), the first and second insulating caplayers (170, 270), the retro-stepped dielectric material portions (165,265), and the dielectric pillar structures 374 and the material of theoutermost layer of the memory films 50 may be introduced into thebackside trenches 79, for example, using an isotropic etch process. Forexample, the sacrificial material layers (142, 242) may include siliconnitride, the materials of the insulating layers (132, 232), the firstand second insulating cap layers (170, 270), the retro-steppeddielectric material portions (165, 265), the dielectric pillarstructures 374, and the outermost layer of the memory films 50 mayinclude silicon oxide materials.

The isotropic etch process may be a wet etch process using a wet etchsolution, or may be a gas phase (dry) etch process in which the etchantis introduced in a vapor phase into the backside trench 79. For example,if the sacrificial material layers (142, 242) include silicon nitride,the etch process may be a wet etch process in which the exemplarystructure is immersed within a wet etch tank including phosphoric acid,which etches silicon nitride selective to silicon oxide, silicon, andvarious other materials used in the art.

Backside recesses (143, 243) may be formed in volumes from which thesacrificial material layers (142, 242) are removed. The backsiderecesses (143, 243) may include first backside recesses 143 that areformed in volumes from which the first sacrificial material layers 142are removed and second backside recesses 243 that are formed in volumesfrom which the second sacrificial material layers 242 are removed. Eachof the backside recesses (143, 243) may be a laterally extending cavityhaving a lateral dimension that is greater than the vertical extent ofthe cavity. In other words, the lateral dimension of each of thebackside recesses (143, 243) may be greater than the height of therespective backside recess (143, 243). A plurality of backside recesses(143, 243) may be formed in the volumes from which the material of thesacrificial material layers (142, 242) is removed. Each of the backsiderecesses (143, 243) may extend substantially parallel to the top surfaceof the substrate semiconductor layer 9. A backside recess (143, 243) maybe vertically bounded by a top surface of an underlying insulating layer(132, 232) and a bottom surface of an overlying insulating layer (132,232). In one embodiment, each of the backside recesses (143, 243) mayhave a uniform height throughout.

Referring to FIG. 22, a backside blocking dielectric layer (not shown)may be optionally deposited in the backside recesses (143, 243) and thebackside trenches 79 and over the first contact level dielectric layer280. The backside blocking dielectric layer includes a dielectricmaterial such as a dielectric metal oxide, silicon oxide, or acombination thereof. For example, the backside blocking dielectric layermay include aluminum oxide. The backside blocking dielectric layer maybe formed by a conformal deposition process such as atomic layerdeposition or chemical vapor deposition. The thickness of the backsideblocking dielectric layer may be in a range from 1 nm to 20 nm, such asfrom 2 nm to 10 nm, although lesser and greater thicknesses may also beused.

At least one conductive material may be deposited in the plurality ofbackside recesses (243, 243), on the sidewalls of the backside trenches79, and over the first contact level dielectric layer 280. The at leastone conductive material may be deposited by a conformal depositionmethod, which may be, for example, chemical vapor deposition (CVD),atomic layer deposition (ALD), electroless plating, electroplating, or acombination thereof. The at least one conductive material may include anelemental metal, an intermetallic alloy of at least two elementalmetals, a conductive nitride of at least one elemental metal, aconductive metal oxide, a conductive doped semiconductor material, aconductive metal-semiconductor alloy such as a metal silicide, alloysthereof, and combinations or stacks thereof.

In one embodiment, the at least one conductive material may include atleast one metallic material, i.e., an electrically conductive materialthat includes at least one metallic element. Non-limiting exemplarymetallic materials that may be deposited in the backside recesses (143,243) include tungsten, tungsten nitride, titanium, titanium nitride,tantalum, tantalum nitride, cobalt, and ruthenium. For example, the atleast one conductive material may include a conductive metallic nitrideliner that includes a conductive metallic nitride material such as TiN,TaN, WN, or a combination thereof, and a conductive fill material suchas W, Co, Ru, Mo, Cu, or combinations thereof. In one embodiment, the atleast one conductive material for filling the backside recesses (143,243) may be a combination of titanium nitride layer and a tungsten fillmaterial.

Electrically conductive layers (146, 246) may be formed in the backsiderecesses (143, 243) by deposition of the at least one conductivematerial. A plurality of first electrically conductive layers 146 may beformed in the plurality of first backside recesses 143, a plurality ofsecond electrically conductive layers 246 may be formed in the pluralityof second backside recesses 243, and a continuous metallic materiallayer (not shown) may be formed on the sidewalls of each backside trench79 and over the first contact level dielectric layer 280. Each of thefirst electrically conductive layers 146 and the second electricallyconductive layers 246 may include a respective conductive metallicnitride liner and a respective conductive fill material. Thus, the firstand second sacrificial material layers (142, 242) may be replaced withthe first and second electrically conductive layers (146, 246),respectively. Specifically, each first sacrificial material layer 142may be replaced with an optional portion of the backside blockingdielectric layer and a first electrically conductive layer 146, and eachsecond sacrificial material layer 242 may be replaced with an optionalportion of the backside blocking dielectric layer and a secondelectrically conductive layer 246. A backside cavity is present in theportion of each backside trench 79 that is not filled with thecontinuous metallic material layer.

Residual conductive material may be removed from inside the backsidetrenches 79. Specifically, the deposited metallic material of thecontinuous metallic material layer may be etched back from the sidewallsof each backside trench 79 and from above the first contact leveldielectric layer 280, for example, by an anisotropic or isotropic etch.Each remaining portion of the deposited metallic material in the firstbackside recesses constitutes a first electrically conductive layer 146.Each remaining portion of the deposited metallic material in the secondbackside recesses constitutes a second electrically conductive layer246. Sidewalls of the first electrically conductive material layers 146and the second electrically conductive layers may be physically exposedto a respective backside trench 79. The backside trenches may have apair of curved sidewalls having a non-periodic width variation along thefirst horizontal direction hd1 and a non-linear width variation alongthe vertical direction.

Each electrically conductive layer (146, 246) may be a conductive sheetincluding openings therein. A first subset of the openings through eachelectrically conductive layer (146, 246) may be filled with memoryopening fill structures 58. A second subset of the openings through eachelectrically conductive layer (146, 246) may be filled with the supportpillar structures 20. Each electrically conductive layer (146, 246) mayhave a lesser area than any underlying electrically conductive layer(146, 246) because of the first and second stepped surfaces. Eachelectrically conductive layer (146, 246) may have a greater area thanany overlying electrically conductive layer (146, 246) because of thefirst and second stepped surfaces.

In some embodiment, drain-select-level isolation structures 72 may beprovided at topmost levels of the second electrically conductive layers246. A subset of the second electrically conductive layers 246 locatedat the levels of the drain-select-level isolation structures 72constitutes drain select gate electrodes. A subset of the electricallyconductive layer (146, 246) located underneath the drain select gateelectrodes may function as combinations of a control gate and a wordline located at the same level. The control gate electrodes within eachelectrically conductive layer (146, 246) are the control gate electrodesfor a vertical memory device including the memory stack structure 55.

Each of the memory stack structures 55 comprises a vertical stack ofmemory elements located at each level of the electrically conductivelayers (146, 246). A subset of the electrically conductive layers (146,246) may comprise word lines for the memory elements. The semiconductordevices in the underlying peripheral device region 700 may comprise wordline switch devices configured to control a bias voltage to respectiveword lines. The memory-level assembly is located over the substratesemiconductor layer 9. The memory-level assembly includes at least onealternating stack (132, 146, 232, 246) and memory stack structures 55vertically extending through the at least one alternating stack (132,146, 232, 246).

Referring to FIGS. 23A-23D, a dielectric material layer may beconformally deposited in the backside trenches 79. The dielectricmaterial layer may include, for example, silicon oxide. Excess portionsof the dielectric material over the first contact level dielectric layer280 may be removed by a planarization process, which may includechemical mechanical planarization (CMP) and/or a recess etch. Eachremaining portion of the dielectric material that fills a backsidetrench 79 constitutes a backside trench fill structure 76, which may bea dielectric wall structure laterally extending along the firsthorizontal direction hd1 and vertically extending through each layerwithin a neighboring pair of alternating stacks {(132, 146), (232, 246)}of insulating layers (132, 232) and electrically conductive layers (146,246). Each sacrificial backside trench fill material structure 77 may bereplaced with a backside trench fill structure 76.

Memory stack structures 55 vertically extend through a respectivealternating stack {(132, 146) and/or (232, 246)} of insulating layers(132, 232) and electrically conductive layers (146, 246). Each of thememory stack structures 55 comprises a respective memory film 50 and arespective vertical semiconductor channel 60. A source region (112, 114,116) is electrically connected to a first end of each of the verticalsemiconductor channels 60, and drain regions is electrically connectedto a second end of a respective one of the vertical semiconductorchannels 60.

Generally, the remaining portions of the sacrificial material layers(142, 242) at the processing steps of FIG. 20 may be replaced with theelectrically conductive layers (146, 246). The electrically conductivelayers (146, 246) comprise a respective strip portion 46S that laterallyextend along the first horizontal direction hd1 between a dielectricpillar structure 374 and a pair of backside trenches 79. The memorystack structures 55 and the electrically conductive layers (146, 246)collectively comprise a two-dimensional array of vertical NAND strings.

Referring to FIG. 24, a photoresist layer 627 may be applied over thefirst contact level dielectric layer 280, and is lithographicallypatterned to form openings within areas of the dielectric pillarstructures 374 and within the areas of the peripheral device region 400that overlie openings through the in-process source-level materiallayers 10 (which contain at least one semiconductor material layer). Ananisotropic etch process may be performed to transfer the pattern of theopenings in the photoresist layer 627 thorough the dielectric pillarstructures 374, through the stack of the first contact-level dielectricmaterial layer 280, the insulating cap layers (170, 270), theretro-stepped dielectric material portions (165, 265), portions of theat least one second dielectric layer 768 within openings through thesource-level material layers 10, and through the silicon nitride layer766 to top surfaces of a subset of the landing-pad-level metal linestructures 788. Array-region contact via cavities 375 may be formedthrough the dielectric pillar structures 374 to a top surface of arespective underlying one of the landing-pad-level metal line structures788. Peripheral region contact via cavities 475 may be formed throughthe retro-stepped dielectric material portions (165, 265) to a topsurface of a respective underlying one of the landing-pad-level metalline structures 788. The photoresist layer 627 may be subsequentlyremoved, for example, by ashing.

Referring to FIG. 25, at least one conductive material is depositedwithin the contact via cavities (375, 475) to form conductive viastructures, which are herein referred to as through-memory-levelconductive via structure (286, 486). The through-memory-level conductivevia structures (286, 486) include array-region through-memory-levelconductive via structures 286 that are formed in the array regioncontact via cavities 375 and peripheral-region through-memory-levelconductive via structures 486 that are formed in the peripheral regioncontact via cavities 475.

In one embodiment, each of the through-memory-level conductive viastructures (286, 486) may include a conductive liner and a conductivefill material. The conductive liner may include a conductive metallicliner such as TiN, TaN, WN, TiC, TaC, WC, an alloy thereof, or a stackthereof. The thickness of the conductive liner may be in a range from 3nm to 30 nm, although lesser and greater thicknesses may also be used.The conductive fill material may include a metal or a metallic alloy.For example, the conductive fill material may include W, Cu, Al, Co, Ru,Ni, an alloy thereof, or a stack thereof.

Each array-region through-memory-level conductive via structure 286vertically extends through, and contacts a sidewall of, a respectivedielectric pillar structure 374. One or more array-regionthrough-memory-level conductive via structure 286 may vertically extendthrough a dielectric pillar structure 374. Each peripheral-regionthrough-memory-level conductive via structure 486 vertically extendsthrough, and contacts a sidewall of, at least one dielectric materialportion such as the first retro-stepped dielectric material portion 165and the second retro-stepped dielectric material portion 265.

Generally, a through-memory-level conductive via structure (such as anarray-region through-memory-level conductive via structure 286) mayvertically extend through a dielectric pillar structure 374. Thethrough-memory-level conductive via structure extends from a firsthorizontal plane located above a topmost layer of the alternating stack(such as a horizontal plane including the top surface of the firstcontact-level dielectric material layer 280) to a second horizontalplane located below a bottommost layer of the alternating stack {(132,146), (232, 246)} (such as a horizontal plane including top surfaces ofthe landing-pad-level metal line structures 788). Thethrough-memory-level conductive via structure may vertically extendthrough an opening through each semiconductor material layer in thesource-level material layers 10, and may contact one of the lower-levelmetal interconnect structures 780.

Referring to FIGS. 26A-26D, a second contact level dielectric layer 282may be formed over the first contact level dielectric layer 280. Thesecond contact level dielectric layer 282 includes a dielectric materialsuch as silicon oxide, and may have a thickness in a range from 100 nmto 600 nm, although lesser and greater thicknesses may also be used.

A photoresist layer (not shown) may be applied over the second contactlevel dielectric layer 282, and may be lithographically patterned toform various contact via openings. For example, openings overlying drainregions 63 and the array-region through-memory-level conductive viastructures 286 may be formed in the memory array region 100, openingsoverlying horizontal surfaces of the stepped surfaces of theelectrically conductive layers (146, 246) may be formed in the staircaseregion 200, and openings overlying the peripheral-regionthrough-memory-level conductive via structures 486 may be formed in theperipheral device region 400. An anisotropic etch process is performedto transfer the pattern in the photoresist layer through the second andfirst contact level dielectric layers (282, 280) and underlyingdielectric material portions. The drain regions 63, the electricallyconductive layers (146, 246), and the through-memory-level conductivevia structure (286, 486) may be used as etch stop structures. Draincontact via cavities may be formed over each drain region 63,staircase-region contact via cavities may be formed over eachelectrically conductive layer (146. 246) at the stepped surfacesunderlying the first and second retro-stepped dielectric materialportions (165, 265), and connection cavities may be formed over thethrough-memory-level conductive via structures (286, 486). Thephotoresist layer may be subsequently removed, for example, by ashing.

At least one conductive material may be deposited within the variouscavities by a conformal deposition process. Excess portions of the atleast one conductive material may be removed from above the horizontalplane including the top surfaces of the second contact-level dielectricmaterial layer 282. Drain conductive via structures 88 are formed in thedrain contact via cavities and on a top surface of a respective one ofthe drain regions 63. Staircase-region conductive via structures 86 areformed in the staircase-region contact via cavities and on a top surfaceof a respective one of the electrically conductive layers (146, 246).The staircase-region conductive via structures 86 may include drainselect level conductive via structures that contact a subset of thesecond electrically conductive layers 246 that function as drain selectlevel gate electrodes. Further, the staircase-region conductive viastructures 86 may include word line conductive via structures thatcontact electrically conductive layers (146, 246) that underlie thedrain select level gate electrodes and function as word lines for thememory stack structures 55. Interconnection via structures 288 may beformed on top of a respective one of the through-memory-level conductivevia structure 286. An array region connection via structure 288 may beformed in each connection cavity that overlies an array regionthrough-memory-level conductive via structure 286. A peripheral regionconnection via structure 488 may be formed in each connection cavitythat overlies a peripheral region through-memory-level conductive viastructure 486. The electrically conductive layers (146, 246) comprise arespective strip portion 46S that laterally extend along the firsthorizontal direction hd1 between a dielectric pillar structure 374 and apair of backside trenches 79.

Referring to FIG. 27, at least one additional dielectric layer may beformed over the contact level dielectric layers (280, 282), andadditional metal interconnect structures (herein referred to asupper-level metal interconnect structures) may be formed in the at leastone additional dielectric layer. For example, the at least oneadditional dielectric layer may include a line-level dielectric layer290 that is formed over the contact level dielectric layers (280, 282).The upper-level metal interconnect structures may include bit lines 98contacting a respective one of the drain conductive via structures 88,and interconnection line structures 96 contacting, and/or electricallyconnected to, at least one of the staircase-region conductive viastructures 86 and/or the array region connection via structures 288and/or the peripheral region connection via structures 488. The bitlines 98 may be electrically connected to a respective subset of thedrain regions 63. In one embodiment, the electrically conductive layers(146, 246) may laterally extend along the first horizontal direction hd1and may have a uniform width along the second horizontal direction hd2.The bit lines 98 may laterally extend along the second horizontaldirection hd2.

In one embodiment, the three-dimensional memory device comprises amonolithic three-dimensional NAND memory device, the electricallyconductive strips (146, 246) comprise, or are electrically connected to,a respective word line of the monolithic three-dimensional NAND memorydevice, the substrate 8 comprises a silicon substrate, the monolithicthree-dimensional NAND memory device comprises an array of monolithicthree-dimensional NAND strings over the silicon substrate, and at leastone memory cell in a first device level of the array of monolithicthree-dimensional NAND strings is located over another memory cell in asecond device level of the array of monolithic three-dimensional NANDstrings. The silicon substrate may contain an integrated circuitcomprising a driver circuit for the memory device located thereon, theelectrically conductive strips (146, 246) comprise a plurality ofcontrol gate electrodes having a strip shape extending substantiallyparallel to the top surface of the substrate 8, the plurality of controlgate electrodes comprise at least a first control gate electrode locatedin the first device level and a second control gate electrode located inthe second device level. The array of monolithic three-dimensional NANDstrings comprises a plurality of vertical semiconductor channels 60,wherein at least one end portion of each of the plurality of verticalsemiconductor channels 60 extends substantially perpendicular to a topsurface of the substrate 8, and one of the plurality of semiconductorchannels including the vertical semiconductor channel 60. The array ofmonolithic three-dimensional NAND strings comprises a plurality ofcharge storage elements (comprising portions of the memory films 50),each charge storage element located adjacent to a respective one of theplurality of vertical semiconductor channels 60.

According to all drawings and various embodiments of the presentdisclosure, a semiconductor structure is provided, which comprises: asemiconductor material layer (which is present within the source-levelmaterial layers 10) overlying a substrate 8; an alternating stack ofinsulating layers (132, 232) and electrically conductive layers (146,246) located over the semiconductor material layer; memory stackstructures 55 vertically extending through the alternating stack; aperipheral circuitry including field effect transistors and located overthe substrate 8 and underneath the semiconductor material layer;lower-level metal interconnect structures 780 formed in lower-leveldielectric material layers 760 and located between the peripheralcircuitry and the semiconductor material layer; a pair of backsidetrench fill structures 76 vertically extending through the alternatingstack and laterally extending along a first horizontal direction hd1; adielectric pillar structure 374 extending through the alternating stackand located between the pair of backside trench fill structures 76,wherein each of the pair of backside trench fill structures 76 and thedielectric pillar structure 374 comprises sidewalls having a bowingprofile that provides a greater width at a height between a topmostlayer of the alternating stack and a bottommost layer of the alternatingstack than at a height of the topmost layer of the alternating stack;and a through-memory-level conductive via structure 286 verticallyextending through the dielectric pillar structure 374 and an opening inthe semiconductor material layer and contacting one of the lower-levelmetal interconnect structures 780.

Embodiments of the present disclosure may be used to form backsidetrenches 79 and the sets of nested trenches (179, 279) using a samelithographic patterning step and a same etch step(s). As such, the setof nested trenches (179, 279) are formed at the same time as neighboringpair of backside trenches 79. The process cost may be reduced byomitting a separate etch step which forms the large size, deeppillar-shaped cavities 379. Furthermore, the chip size may be reduced byusing smaller tolerances between the backside trench 79 andpillar-shaped cavity 379 because they are formed during the samelithography step. Sequential removal of sacrificial inner trench fillstructures 177, vertically alternating sequences of insulating plates(132′ and/or 232′) and sacrificial material plates (142′ and/or 242′),and sacrificial outer trench fill structures 277 may be performed usinga block level lithography process (such as a mid-ultravioletlithographic patterning process) and low cost etch processes such as wetetch processes. Thus, the processing cost for forming pillar-shapedcavities 379 and dielectric pillar structures 374 between neighboringpairs of backside trenches may be significantly reduced through the useof the methods of the embodiments of the present disclosure. Thesidewalls of the backside trenches 79 and the sidewalls of the nestedtrenches (179, 279) may have same bulging profiles due to use of a sameanisotropic etch process.

Although the foregoing refers to particular embodiments, it will beunderstood that the disclosure is not so limited. It will occur to thoseof ordinary skill in the art that various modifications may be made tothe disclosed embodiments and that such modifications are intended to bewithin the scope of the disclosure. Compatibility is presumed among allembodiments that are not alternatives of one another. The word“comprise” or “include” contemplates all embodiments in which the word“consist essentially of” or the word “consists of” replaces the word“comprise” or “include,” unless explicitly stated otherwise. Where anembodiment using a particular structure and/or configuration isillustrated in the present disclosure, it is understood that the presentdisclosure may be practiced with any other compatible structures and/orconfigurations that are functionally equivalent provided that suchsubstitutions are not explicitly forbidden or otherwise known to beimpossible to one of ordinary skill in the art. All of the publications,patent applications and patents cited herein are incorporated herein byreference in their entirety.

What is claimed is:
 1. A semiconductor structure, comprising: asemiconductor material layer overlying a substrate; an alternating stackof insulating layers and electrically conductive layers located over thesemiconductor material layer; memory stack structures verticallyextending through the alternating stack; a peripheral circuitryincluding field effect transistors and located on the substrate andunderneath the semiconductor material layer, wherein the peripheralcircuitry is configured to control charge storage elements within thememory stack structures; lower-level metal interconnect structuresformed in lower-level dielectric material layers and located between theperipheral circuitry and the semiconductor material layer; a pair ofbackside trench fill structures vertically extending through thealternating stack and laterally extending along a first horizontaldirection; a dielectric pillar structure extending through thealternating stack and located between the pair of backside trench fillstructures, wherein each of the pair of backside trench fill structuresand the dielectric pillar structure comprises sidewalls having a bowingprofile that provides a greater width at a height between a topmostlayer of the alternating stack and a bottommost layer of the alternatingstack than at a height of the topmost layer of the alternating stack;and a through-memory-level conductive via structure vertically extendingthrough the dielectric pillar structure and an opening in thesemiconductor material layer and contacting one of the lower-level metalinterconnect structures.